assembly problem solving

Assembly exercises

Exercises not as directly relevant to this year’s class are marked with ⚠️.

ASM-1. Disassemble

Here’s some assembly produced by compiling a C program.

QUESTION ASM-1A. How many arguments might this function have? Circle all that apply.

All (1–4). The function has no arguments that it uses , but it might have arguments it doesn’t use.

QUESTION ASM-1B. What might this function return? Circle all that apply.

• Its first argument, whatever that argument is
• A square number other than 0 or 1
• None of the above

It can only return 1.

QUESTION ASM-1C. Which callee-saved registers does this function save and restore? Circle all that apply.

The callee-saved registers are %rbx, %rbp, %rsp, and %r12-%r15. The code does not modify any of these registers, so it doesn’t “save and restore” them either.

QUESTION ASM-1D. This function handles signed integers. If we changed the C source to use unsigned integers instead, which instructions would change? Circle all that apply.

jl We accepted circled imull or not! Although x86 imull is signed, as used in C it behaves equivalently to the nominally-unsigned mull , and some compilers use imull for both kinds of integer. From the Intel manuals: “[These] forms [of imul ] may also be used with unsigned operands because the lower half of the product is the same regardless if the operands are signed or unsigned. The CF and OF flags, however, cannot be used to determine if the upper half of the result is non-zero.”

QUESTION ASM-1E. What might this function print? Circle all that apply.

Choice #3 ( 3 4 ) only. The function searches for a solution to x 2 + y 2 == z 2 , under the constraint that x ≤ y . When it finds one, it prints x and y and then returns. It always starts from 1 1 and increments x and y one at a time, so it can only print 3 4 .

ASM-2. Assembly

Here is some x86 assembly code.

QUESTION ASM-2A. Write valid C code that could have compiled into this assembly (i.e., write a C definition of function f ), given the global variable declarations “ extern unsigned a, b; .” Your C code should compile without warnings. REMINDER: You are not permitted to run a C compiler, except for the C compiler that is your brain.

void f () { a -= b & 255 ; } Or see below for more possibilities.

QUESTION ASM-2B. Write different valid, warning-free C code that could have compiled into that assembly. This version should contain different operators than your first version. (For extra credit, use only one operator .)

void f () { a += - (b % 256 ); }

QUESTION ASM-2C. Again, write different valid, warning-free C code that could have compiled into that assembly. In this version, f should have a different type than in your first version.

unsigned f () { a = a - b % 0x100 ; return a; } unsigned f () { a -= ( unsigned char ) b; return a; } char * f ( int x, int y, int z[ 1000 ]) { a -= ( unsigned char ) b; return ( char * ) a; }

ASM-3. Assembly and Data Structures

For each code sample below, indicate the most likely type of the data being accessed. (If multiple types are equally likely, just pick one.)

QUESTION ASM-3A. movzbl %al, %eax

unsigned char

QUESTION ASM-3B. movl -28(%rbp), %edx

int or unsigned

QUESTION ASM-3C. movsbl -32(%rbp), %eax

[signed] char

QUESTION ASM-3D. movzwl -30(%rbp), %eax

unsigned short

For each code sample below, indicate the most likely data structure being accessed (assume that g_var is a global variable). Be as specific as possible.

QUESTION ASM-3E. movzwl 6(%rdx,%rax,8), %eax

unsigned short in an array of 8-byte structures

QUESTION ASM-3F. movl (%rdx,%rax,4), %eax

Array of int s or unsigned int s

QUESTION ASM-3G.

char field from a structure; or the 4th character in a string

For the remaining questions, indicate for what values of the register contents will the jump be taken.

QUESTION ASM-3H.

QUESTION ASM-3I.

Any odd value (the fact that we're only looking at the lowest byte is pretty irrelevant)

QUESTION ASM-3J.

When %eax is less than %edx , considered as signed integers

ASM-4. Assembly language

The next four questions pertain to the following four code samples.

f1 f1: subq $8 , %rsp call callfunc movl %eax , %edx leal 1 ( %rax , %rax , 2 ), %eax testb $1 , %dl jne .L3 movl %edx , %eax shrl $31 , %eax addl %edx , %eax sarl %eax .L3: addq $8 , %rsp ret

f2 f2: pushq %rbx xorl %ebx , %ebx .L3: movl %ebx , %edi addl $1 , %ebx call callfunc cmpl $10 , %ebx jne .L3 popq %rbx ret

f3 f3: subq $8 , %rsp call callfunc subl $97 , %eax cmpb $4 , %al ja .L2 movzbl %al , %eax jmp *. L4 (, %rax , 8 ) .L4: .quad .L3 .quad .L9 .quad .L6 .quad .L7 .quad .L8 .L3: movl $42 , %edx jmp .L5 .L6: movl $4096 , %edx jmp .L5 .L7: movl $52 , %edx jmp .L5 .L8: movl $6440 , %edx jmp .L5 .L2: movl $0 , %edx jmp .L5 .L9: movl $61 , %edx .L5: movl $.LC0 , %esi movl $1 , %edi movl $0 , %eax call __printf_chk addq $8 , %rsp ret .LC0: .string "Sum = %d\n"

f4 f4: subq $40 , %rsp movl $1 , ( %rsp ) movl $0 , 16 ( %rsp ) .L2: leaq 16 ( %rsp ), %rsi movq %rsp , %rdi call callfunc movl 16 ( %rsp ), %eax cmpl %eax , ( %rsp ) jne .L2 addq $40 , %rsp ret

Now answer the following questions. Pick the most likely sample; you will use each sample exactly once.

QUESTION ASM-4A. Which sample contains a for loop?

QUESTION ASM-4B. Which sample contains a switch statement?

QUESTION ASM-4C. Which sample contains only an if/else construct?

QUESTION ASM-4D. Which sample contains a while loop?

ASM-5. Calling conventions: 6186

University Professor Helen Vendler is designing a poetic new processor, the 6186. Can you reverse-engineer some aspects of the 6186’s calling convention from its assembly?

Here’s a function:

And here’s that function compiled into 6186 instructions.

6186 assembly syntax is based on x86-64 assembly, and like the x86-64, 6186 registers are 64 bits wide. However, the 6186 has a different set of registers. There are just five general-purpose registers, %ra , %rb , %rr , %rx , and %ry . (“[W]hen she tries to be deadly serious she is speaking under…constraint”.) The example also features the stack pointer register, %rsp .

Give brief explanations if unsure.

QUESTION ASM-5A. Which register holds function return values?

QUESTION ASM-5B. What is sizeof(int) on the 6186?

QUESTION ASM-5C. Which general-purpose register(s) must be callee-saved?

QUESTION ASM-5D. Which general-purpose register(s) must be caller-saved?

%rr , %ra , %rx

QUESTION ASM-5E. Which general-purpose register(s) might be callee-saved or caller-saved (you can’t tell which)?

QUESTION ASM-5F. Assuming the compiler makes function stack frames as small as possible given the calling convention, what is the alignment of stack frames?

QUESTION ASM-5G. Assuming that the 6186 supports the same addressing modes as the x86-64, write a single instruction that has the same effect on %ra as these three instructions:

movl 4(%ra,%rx,8), %ra

ASM-6. Data structure assembly

Here are four assembly functions, f1 through f4 .

f1: pushq %rbp movq %rsp , %rbp testl %esi , %esi jle LBB0_3 incl %esi LBB0_2: movq 8 ( %rdi ), %rdi decl %esi cmpl $1 , %esi jg LBB0_2 LBB0_3: movl ( %rdi ), %eax popq %rbp retq

f2: pushq %rbp movq %rsp , %rbp movslq %esi , %rax movq ( %rdi , %rax , 8 ), %rcx movl ( %rcx , %rax , 4 ), %eax popq %rbp retq

f3: testl %esi , %esi jle LBB2_3 incl %esi LBB2_2: movl %edx , %eax andl $1 , %eax movq 8 ( %rdi , %rax , 8 ), %rdi sarl %edx decl %esi cmpl $1 , %esi jg LBB2_2 LBB2_3: movl ( %rdi ), %eax retq

f4: movslq %esi , %rax movl ( %rdi , %rax , 4 ), %eax retq

QUESTION ASM-6A. Each function returns a value loaded from some data structure. Which function uses which data structure?

• Array of pointers to arrays
• Linked list
• Binary tree

Array— f4 ; Array of pointers to arrays— f2 ; Linked list— f1 ; Binary tree— f3

QUESTION ASM-6B. The array data structure is an array of type T. Considering the code for the function that manipulates the array, which of the following types are likely possibilities for T? Circle all that apply.

• unsigned long
• unsigned long long

ASM-7. Where’s Waldo?

In the following questions, we give you C code and a portion of the assembly generated by some compiler for that code. (Sometimes we blank out a part of the assembly.) The C code contains a variable, constant, or function called waldo , and a point in the assembly is marked with asterisks *** . Your job is to find Waldo: write an assembly expression or constant that holds the value of waldo at the marked point. We’ve done the first one for you.

NON-QUESTION : Where’s Waldo?

ANSWER : %edi , -0x4(%rbp) , %eax , and %rax all hold the value of waldo at the marked point, so any of them is a valid answer. If the asterisks came before the first instruction, only %edi would work.

QUESTION ASM-7A : Where’s Waldo?

QUESTION ASM-7B : Where’s Waldo?

QUESTION ASM-7C : Where’s Waldo?

(%rdi,%rsi,8)

QUESTION ASM-7D : Where’s Waldo?

QUESTION ASM-7E : Where’s Waldo?

QUESTION ASM-7F : Where’s Waldo?

⚠️ This question currently uses 32-bit assembly.

In the remaining questions, you are given assembly compiled from one of the above functions by a different compiler, or at a different optimization level. Your goal is to figure out what C code corresponds to the given assembly.

QUESTION ASM-7G :

What’s Waldo? Circle one.

• permutation_compare
• binary_search

5, factorial

QUESTION ASM-7H :

QUESTION ASM-7I :

ASM-8. (removed because redundant)

Asm-9. disassembly ii.

The questions in this section concern a function called ensmallen , which has the following assembly.

QUESTION ASM-9A. How many arguments is this function likely to take? Give line numbers that helped you determine an answer.

2, because of lines 1 & 3

QUESTION ASM-9B. Are the argument(s) pointers? Give line numbers that helped you determine an answer.

Yes, because of lines 1, 3, 9, 14

QUESTION ASM-9C. What type(s) are the argument(s) likely to have? Give line numbers that helped you determine an answer.

unsigned char* . Lines 1, 3, 9, and 14 are byte -moving instructions. The z in movzbl (Lines 1 and 9) indicates z ero-extension, i.e., unsigned char . But char* is possible too; the characters are only compared for equality with each other (Line 10) or zero (Lines 2/4 and 13/15), so we can’t really distinguish signed from unsigned.

QUESTION ASM-9D. Write a likely signature for the function. Use return type void .

void ensmallen ( unsigned char * a, unsigned char * b);

QUESTION ASM-9E. Write an alternate likely signature for the function, different from your last answer. Again, use return type void .

void ensmallen ( unsigned char * a, const unsigned char * b); void ensmallen ( char * a, char * b); void ensmallen ( void * dst, const void * src); etc., etc.

QUESTION ASM-9F. Which callee-saved registers does this function use? Give line numbers that helped you determine an answer.

None except possibly %rsp (no callee-saved registers are referenced in the code).

QUESTION ASM-9G. The function has an “input” and an “output”. Give an “input” that would cause the CPU to jump from line 5 to label .L23 , and describe what is placed in the “output” for that “input”.

The input is an empty string ( "" ), and the function puts an empty string in the output. You might think the function’s output was the value of its %eax register what it returned. But remember that functions without return values can also use %eax, and we told you above that this function’s return type is void ! ensmallen ’s “output” is most likely the string pointed to by its first parameter. In that sense ensmallen is sort of like strcpy or memcpy .

QUESTION ASM-9H. Give an “input” for which the corresponding “output” is not a copy of the “input”. Your answer must differ from the previous answer.

"aaaa" (output is "a" ); any string that has adjacent characters that are the same

QUESTION ASM-9I. Write C code corresponding to this function. Make it as compact as you can.

void ensmallen ( char * dst, const char * src) { while (( * dst = * src)) { while ( * dst == * src) ++ src; ++ dst; } } Or, a little less compactly: void ensmallen ( char * dst, const char * src) { while ( * src) { * dst = * src; while ( * src == * dst) ++ src; ++ dst; } * dst = 0 ; }

ASM-10. Machine programming

Intel really messed up this time. They’ve released a processor, the Fartium Core Trio, where every instruction is broken except the ones on this list.

(In case you forgot, xchgq swaps two values—here, the values in two registers—without modifying condition codes.)

“So what if it’s buggy,” says Andy Grove; “it can still run programs.” For instance, he argues convincingly that this function:

is implemented correctly by this Fartium instruction sequence:

Your job is to implement more complex functions using only Fartium instructions. Your implementations must have the same semantics as the C functions, but may perform much worse than one might expect. You may leave off arguments and write instruction numbers (#1–10) or instruction names. Indicate where labels L1–L3 point (if you need them). Assume that the Fartium Core Trio uses the normal x86-64 calling convention.

QUESTION ASM-10A.

xorq %rax, %rax; retq . %rax has unknown value when a function begins, so we need to clear it.

QUESTION ASM-10B.

xchgq %rdi, %rax; retq .

QUESTION ASM-10C.

L3: jmp L3 .

QUESTION ASM-10D.

xorq %rax , %rax incq %rax incq %rax movl ( %rdi , %rax , 4 ), %edi xchgl %rax , %rdi ret

So much for the easy ones. Now complete one out of the following parts, or more than one for extra credit.

QUESTION ASM-10E.

xorq %rax , %rax # %rax := 0 xchgq %rax , %rdi # now %rax == a and %rdi == 0 L3 : cmpq %rdi , %rsi # compare %rsi and %rdi (which is 0) je L1 # "if %rsi == 0 goto L1" incl %rax # ++%rax decl %rsi # --%rsi jmp L3 L1: retq The loop at L3 executes b times, incrementing %eax each time. Here’s morally equivalent C++: long add ( long a, long b) { while (b != 0 ) { ++ a; -- b; } return a; }

QUESTION ASM-10F.

xorq %rax , %rax # %rax := 0 L3 : xchgq %rax , %rdi cmpl %rdi , %rsi xchgq %rax , %rdi je L1 # "if %rax == i goto L1" incq %rax # ++%rax jmp L3 L1: movl ( %rdi , %rax , 4 ), %edi # %edi := a[i] xchgq %rax , %rdi ret

ASM-11. Program Layout

For the following questions, select the part(s) of memory from the list below that best describes where you will find the object.

• between the heap and the stack
• in a read-only data segment
• in a text segment starting at address 0x08048000
• in a read/write data segment
• in a register

Assume the following code, compiled without optimization.

QUESTION ASM-11A. The string "fib(%lu) = %lu\n" (line 37).

Read-only data segment, aka text segment

QUESTION ASM-11B. optind (line 23).

Read/write data segment

QUESTION ASM-11C. When executing at line 5, where you will find the address to which fib returns.

QUESTION ASM-11D. Where will you find the value of EOF that is compared to the return value of getopt in line 14.

Register—although this register is likely to be hidden inside the processor, not one of the ones that have programmable names. Alternately, text segment, since the −1 will be encoded into some instruction.

QUESTION ASM-11E. getopt (line 14)

Text segment; alternately: Between the heap and the stack (because that’s where shared libraries tend to be loaded)

QUESTION ASM-11F. fib (lines 1-6)

Text segment

QUESTION ASM-11G. the variable f (line 36)

Register or stack

QUESTION ASM-11H. the string being passed to strtoul (line 30)

QUESTION ASM-11I. strdup (line 30)

Text segment or between heap & stack (same as getopt )

QUESTION ASM-11J. The value of the fib function when we return from fib (line 5).

Register (%rax)

ASM-12. Assembly and Data Structures

Consider the following assembly function.

QUESTION ASM-12A. How many parameters does this function appear to have?

QUESTION ASM-12B. What do you suppose the type of that parameter is?

const char* (or const unsigned char* , char* , etc.)

QUESTION ASM-12C. Write C++ code that corresponds to it.

It’s strlen ! int strlen ( const char * x) { int n = 0 ; for (; * x; ++ x) ++ n; return n; }

ASM-13. Assembly language

Consider the following four assembly functions.

# Code Sample 1 movq %rdi , %rax testq %rdx , %rdx je .L2 addq %rdi , %rdx movq %rdi , %rcx .L3: addq $1 , %rcx movb %sil , - 1 ( %rcx ) cmpq %rdx , %rcx jne .L3 .L2: rep ret

# Code Sample 2 movq %rdi , %rax testq %rdx , %rdx je .L2 addq %rdi , %rdx movq %rdi , %rcx .L3: addq $1 , %rcx addq $1 , %rsi movzbl - 1 ( %rsi ), %r8d movb %r8b , - 1 ( %rcx ) cmpq %rdx , %rcx jne .L3 .L2: rep ret

# Code Sample 3 movb ( %rsi ), %al testb %al , %al je .L3 incq %rsi .L2: movb %al , ( %rdi ) incq %rdi movb ( %rsi ), %al incq %rsi testb %al , %al jne .L2 .L3: movq %rdi , %rax ret

# Code Sample 4 testq %rdx , %rdx je .L3 movq %rdi , %rax .L2: movb %sil , ( %rax ) incq %rax decq %rdx jne .L2 .L3: movq %rdi , %rax ret

( Note: The %sil register is the lowest-order byte of register %rsi , just as %al is the lowest-order byte of %rax and %r8b is the lowest-order byte of %r8 .)

QUESTION ASM-13A. Which two of the assembly functions perform the exact same task?

QUESTION ASM-13B. What is that task? You can describe it briefly, or give the name of the corresponding C library function.

QUESTION ASM-13C. Explain how the other two functions differ from each other.

One is memcpy and the other is strcpy , so the difference is that #2 terminates after copying a number of bytes indicated by the parameter while the other terminates when it encounters a NUL value in the source string.

ASM-14. Golden Baron

A very rich person has designed a new x86-64-based computer, the Golden Baron Supercomputer 9000, and is paying you handsomely to write a C compiler for it. There’s just one problem. This person, like many very rich people, is dumb, and on their computer, odd-numbered memory addresses don’t work for data. When data is loaded into a general-purpose register from an odd-numbered address, the value read is zero. For example, consider the following instructions:

(where the address of a is even). Executed on true x86-64, %rax will hold the value 0x01020304; on Golden Baron, %rax will hold 0x00020004.

But it is still possible to write a correct C compiler for this ungodly hardware—you just have to work around the bad memory with code. You plan to use two bytes of Golden Baron memory for every one byte of normal x86-64 memory. For instance, an array int a[2] = {1, 0x0a0b0c0d}; would be stored in 16 bytes of memory, like so:

Pointer arithmetic, and moving multi-byte values to and from registers, must account for the zero bytes that alternate with meaningful bytes. So to read the correct value for a[2] , the compiler must arrange to read the bytes at addresses A+8 , A+10 , A+12 , and A+14 , where A is the address of the first byte in a .

QUESTION ASM-14A. What should printf("%zu\n", sizeof(char)) print on Golden Baron?

1. This is required by the C++ abstract machine: sizeof(char) == 1 .

QUESTION ASM-14B. This function

can compile to two instructions on x86-64, including retq . It can also compile to two instructions on Golden Baron. (We’re assuming that memory used for Golden Baron instructions works normally.) What are those instructions?

movsbl ( %rdi , %rsi , 2 ), %eax retq

QUESTION ASM-14C. This function

can compile to two instructions on x86-64, but Golden Baron requires more work. Write the Golden Baron translation of this function in x86-64 assembly language. For partial credit, write C code that, executed on x86-64, would return the correct value from a Golden Baron-formatted array.

movzbl ( %rdi , %rsi , 8 ), %eax movzbl 2 ( %rdi , %rsi , 8 ), %ecx shll $8 , %ecx orl %ecx , %eax movzbl 4 ( %rdi , %rsi , 8 ), %ecx shlq $16 , %ecx orl %ecx , %eax movzbl 8 ( %rdi , %rsi , 8 ), %ecx shlq $24 , %ecx orl %ecx , %eax retq Or: movq ( %rdi , %rsi , 8 ), %rcx movq %rcx , %rax andq $255 , %rax shrq $8 , %rcx movq %rcx , %rdx andq $0xff00 , %rdx orl %edx , %eax shrq $16 , %rcx movq %rcx , %rdx andq $0xff0000 , %rdx orl %edx , %eax shrq $32 , %rcx movq %rcx , %rdx andq $0xff000000 , %rdx orl %edx , %eax retq

QUESTION ASM-14D. The Golden Baron’s x86-64 processor actually supports a secret instruction, swizzleq SRC, REG , which rearranges the nybbles (the hexadecimal digits—the aligned 4-bit slices) of the destination register REG based on the source argument SRC . Here’s some examples. Assuming that %rax holds the value 0x0123456789ABCDEF , the following swizzleq instructions leave the indicated results in %rax :

swizzleq $0, %rax : %rax gets 0xFFFF'FFFF'FFFF'FFFF .

The contents of nybble 0 [bits 0-3, inclusive], are repeated into every nybble.

swizzleq $0xFEDCBA9876543210, %rax : %rax gets 0x0123'4567'89AB'CDEF .

Each nybble is mapped to its current value: nybble 0 [bits 0-3] is placed in nybble 0 [bits 0-3], nybble 1 in nybble 1, and so forth.

swizzleq $0x0123456701234567, %rax : %rax gets 0xFEDC'BA98'FEDC'BA98 .

Nybble 0 [bits 0-3] is placed in nybbles 7 and 15 [bits 28-31 and 60-63]; nybble 1 [bits 4-7] is placed in nybbles 6 and 14 [bits 24-27 and 56-59]; etc.

swizzleq $0xEFCDAB8967452301, %rax : %rax gets 0x1032'5476'98BA'DCFE .

The nybbles of each byte are exchanged.

Use swizzleq to shorten your answer for Part C.

movq ( %rdi , %rsi , 8 ), %rax swizzleq $0x2222 ' 2222 ' dc98 ' 5410 , %rax retq

ASM-15. Instruction behavior

QUESTION ASM-15A. Name three different x86-64 instructions that always modify the stack pointer, no matter their arguments (instruction names only; suffixes don’t count, so movl and movq are the same instruction name).

push , pop , call , ret

QUESTION ASM-15B. Name three different x86-64 instructions that sometimes modify the stack pointer, depending on their arguments.

mov , add , sub , or , and , …

QUESTION ASM-15C. Name three different x86-64 instructions that never modify the stack pointer, no matter their arguments.

jmp , jne , je , jWHATEVER , cmp , test , nop , many others

QUESTION ASM-15D. List three different instructions, including arguments, that if placed immediately before a retq instruction that ends a function, will never change the function’s behavior. The instructions should have different names. No funny business: assume the function was compiled from valid C, that relative jumps are fixed up, and that, for example, it doesn’t access its own code.

Many examples: retq :) jmp [next instruction] test (any register), (any register) cmp (any register), (any register) nop mov s or arithmetic instructions that involve caller-saved registers other than %rax

ASM-16. Calling convention

The following questions concern valid C++ functions compiled using the normal x86-64 calling convention. True or false?

QUESTION ASM-16A. If the function’s instructions do not save and restore any registers, then the C++ function did not call any other function.

False for two reasons: (1) If this function doesn’t use any callee-saved registers, it doesn't need to explicitly save & restore anything. (2) Tail call elimination.

QUESTION ASM-16B. If the function’s instructions do not change the stack pointer, then the function’s instructions do not contain a call instruction.

True because of stack alignment.

QUESTION ASM-16C. If the function’s instructions do not change the stack pointer, then the C++ function did not call any other function. Explain your answer briefly.

False because of tail call elimination.

QUESTION ASM-16D. If the function’s instructions do not modify the %rax register, then the C++ function must return void .

False; the function could return the result of calling another function.

QUESTION ASM-16E. If the function’s instructions store a local variable on the stack, then that variable’s address will be less than the function’s initial stack pointer.

ASM-17. Assembly

Here are three x86-64 assembly functions that were compiled from C.

f1: xorl %eax , %eax L2: movsbq ( %rdi ), %rdx subq $48 , %rdx cmpq $9 , %rdx ja L5 imulq $10 , %rax , %rax incq %rdi addq %rdx , %rax jmp L2 L5: ret

f2: movq %rdi , %rax L7: cmpb $0 , ( %rax ) je L9 incq %rax jmp L7 L9: cmpq %rax , %rdi jnb L11 decq %rax movb ( %rdi ), %cl incq %rdi movb ( %rax ), %dl movb %cl , ( %rax ) movb %dl , - 1 ( %rdi ) jmp L9 L11: ret

f3: xorl %eax , %eax L13: cmpq %rax , %rdx je L15 movb ( %rdi , %rax ), %cl movb ( %rsi , %rax ), %r8b movb %r8b , ( %rdi , %rax ) movb %cl , ( %rsi , %rax ) incq %rax jmp L13 L15: ret

( Note: imulq $10, %rax, %rax means %rax *= 10 .)

QUESTION ASM-17A. How many arguments does each function most likely take?

f1 —1, f2 —1, f3 —3

QUESTION ASM-17B. Which functions modify at least one caller-saved register? List all that apply or write “none”.

All of them

QUESTION ASM-17C. Which functions never modify memory? List all that apply or write “none”.

QUESTION ASM-17D. Write a signature for each function, giving a likely type for each argument and a likely return type. (You may give a void return type if you think the function doesn’t return a useful value.)

long f1 ( const char * ); void f2 ( char * ); void f3 ( char * , char * , size_t);

QUESTION ASM-17E. One of these functions swaps the contents of two memory regions. Which one?

QUESTION ASM-17F. What is the value of %rax in f2 the first time L9 is reached? Write a C expression in terms of f2 ’s argument or arguments; you may use standard library functions.

%rdi + strlen(%rdi)

QUESTION ASM-17G. Give arguments for each function that would result in the function returning without writing to memory or causing a fault.

f1("") , f2("") , f3("", "", 0)

QUESTION ASM-17H. Complete this function so that it returns the number

• For full credit, use only calls to f1 , f2 , and f3 . For partial credit, do something simpler.

int magic () { … f2(s1); f3(s1, s3, 2 ); return f1(s3); }

ASM-18. Kernel assembly

Helen found the following assembly code while hacking a WeensyOS-like kernel . She would like to figure out what the function is doing.

Hexadecimal reference: 4095 == 0xFFF ; 4096 == 0x1000 ; -4096 == 0xFFFFFFFFFFFFF000 ; 4088 == 0xFF8 .

QUESTION ASM-18A. How many arguments does the function take, assuming that there are no unused arguments?

2 arguments. %rdi and %rsi . 2 pts

QUESTION ASM-18B. What does this function return if it encounters a situation that leads to “ error ”?

Helen realizes that the compiler performed some optimizations that made the code somewhat obscure. For example, these instructions contain constants not present in the C++ source:

QUESTION ASM-18C. Which of the following snippets is equivalent to the snippet above? List all that apply.

• shrq $33 , %rax andl $511 , %eax movq ( %rdi , %rax , 8 ), %rax
• shrq $39 , %rax andl $511 , %eax movq ( %rdi , %rax , 8 ), %rax
• shrq $39 , %rax andl $511 , %eax movq ( %rdi , %rax , 4 ), %rax
• shrq $33 , %rax andl $511 , %eax movq ( %rdi , %rax , 4 ), %rax

QUESTION ASM-18D. If rdi and rax were C++ variables corresponding to %rdi and %rax , what would be their likely types?

unsigned long* , unsigned long 4 pts

QUESTION ASM-18E. Please write one line of C++ code, using variables rdi and rax , that could compile into the 3 lines of assembly code we are currently investigating.

rax = rdi[(rax >> 39 ) & 0x1FF ]; 2 pts

QUESTION ASM-18F. How many bits of this function’s second argument are used?

QUESTION ASM-18G. Helen notes that the code contains four copies of a pattern of instructions with different constants. After connecting these constants with CS 61 concepts, she’s able to tell what the function does without deciphering every line of assembly.

Use a single concise sentence to describe the high-level functionality of this function.

Something like "To walk the page table." or "To translate a virtual address to a physical address given an L4 page table." 1 pt

ASM-19. Calling convention and optimizations

QUESTION ASM-19A. Some aspects of the x86-64 calling convention are conventional, meaning that different operating systems could easily make different choices. Others are more fundamental in that they are built in to the x86-64 instruction set. Which of the following aspects of the calling convention are truly conventional (different operating systems could easily make different choices)? List all that apply.

• The stack grows down
• %rsp is a callee-saved register
• %rbx is a callee-saved register
• %rbp is a callee-saved register
• The first argument register is %rdi
• The second argument register is %rsi
• The return register is %rax

2pts 1, 2 are not conventional: The call / ret and push / pop instructions enforce these. 3-7 are conventional.

QUESTION ASM-19B. We saw the compiler sometimes place loop variables in callee-saved registers. For example, here:

the i , n , and sum objects were stored in callee-saved registers %rbx , %r12 , and %rbp , respectively. Describe a situation when this choice has a meaningful chance of boosting the overall performance of f .

2pts A meaningful chance of performance improvement occurs if g doesn’t use any callee-saved registers. If f chose caller-saved registers, i/n/sum would be saved & restored n times by f . If f chose callee-saved registers and g used those registers, i/n/sum would be saved & restored n times by g (so the same number of save/restore pairs). If f chose callee-saved registers and g did not use them, i/n/sum would be saved & restored 0 times.

QUESTION ASM-19C. Write two substantively different C++ functions that could compile to the same assembly on x86-64. (“Substantively different” means you can’t just change the function’s name and types.)

3pts Some examples: int f1a () { return 0 ; } int f1b () { return 1 - 1 ; } int f2a ( int a, int b) { if (a > 0 ) { return f2a(a - 1 , b + a); } else { return b; } } int f2b ( int a, int b) { while (a > 0 ) { b += a; a -= 1 ; } return b; }

QUESTION ASM-19D. Which of the following properties of a function could you reliably infer from compiler-generated assembly? List all that apply; assume the function’s name is not provided, and that the function does not call any other functions. Explain briefly if unsure.

• The types of its arguments
• Whether it can dereference a pointer argument
• Whether it can use at least one of its arguments
• Whether it has unused arguments

3pts 2, 3. We can’t reliably infer types because operations on different types often compile to the same instructions. We can’t reliably infer unused arguments, either; a function f(int a, int b) that doesn’t use b will often have the same assembly as f(int a) . But 2 and 3 can be reliably inferred. Dereferencing a pointer (e.g., movq (%rdi), %rax ) is unambiguous in assembly. We also know the calling convention and can detect whether an argument-passing register is ever used with its entry-time value. (Many students raised questions during the exam regarding the wording of this question.)

ASM-20. Bignums

x86-64 processors have built-in support for integers of up to 64 bits. For larger integers, we must turn to software. This simple “bignum” type represents a 128-bit unsigned integer.

If bignum bn represents 2 65 , then hex_print_bignum(bn) will print 0x20000000000000000 (that’s a 2 followed by 16 zeros).

QUESTION ASM-20A. Does bignum use a big-endian representation, a little-endian representation, or a mix?

3pts Little-endian: the lowest-order bits come first in the structure (have lower addresses).

QUESTION ASM-20B. Complete the following function, which returns true iff a > b .

3pts return a.y > b.y || (a.y == b.y && a.x > b.x) .

QUESTION ASM-20C. Complete the following function, which returns the sum a + b . (You may use the fact that if x and y are unsigned integers using computer arithmetic, then the addition z = x + y overflows iff z < x || z < y .)

3pts bignum bignum_add (bignum a, bignum b) { bignum ret = { a.x + b.x, a.y + b.y }; if (ret.x < a.x || ret.x < b.x) { ret.y += 1 ; } return ret; } Note that the question had a bug in it in some versions, where the overflow condition was given as “ z < x && z < y ”. Sorry! We didn’t take off points for that error.

QUESTION ASM-20D. Complete the same function in x86-64 assembly . Thanks to the calling convention, this function behaves as if the signature were as follows:

You may translate your C++ code directly, or you may use the x86-64 CF carry flag and associated instructions to simplify the translation.

3pts bignum_add: movq %rsi , %eax addq %rcx , %eax movq %eax , ( %rdi ) jnc .L1 xorq %eax , %eax addq $1 , %eax jmp .L2 .L1: xorq %eax , %eax .L2: addq %rdx , %eax addq %r8 , %eax movq %eax , $8 ( %rdi ) movq %rdi , %eax retq

ASM-21. Disassembly

Consider the following function in assembly:

QUESTION ASM-21A. True or False:

• The function likely takes 2 arguments.
• The function accesses 4-byte integer values in primary memory.
• The function likely works with signed integers.
• There is likely a loop in the function.
• The register %eax likely contains a loop index (a value updated by a fixed amount on each loop iteration).

3pts . +2 for 1/2 wrong, +1 for 3/4 wrong. True; it uses %rdi and %rsi but no other argument registers False; it does not access primary memory for data. False; it uses jb (unsigned less-than) rather than jl . True. False; %eax is updated by a variable amount on each iteration.

QUESTION ASM-21B. Give a input to this function such that it never returns.

2pts A postive integer and a zero.

QUESTION ASM-21C. How would you modify the function, in assembly, such that it eventually returns for all inputs?

2pts Add on top: test %edi , %edi je .L2 test %esi , %esi je .L2 Or add on top, retq ;)

QUESTION ASM-21D. Give one set of arguments for which the function terminates, and the corresponding return value.

3pts The function is greatest-common-divisor.

ASM-22. Buffer overflows

QUESTION ASM-22A. Give argument(s) to function _Z4buf1PKc , including types and values, that would cause a buffer overflow that overwrote at least part of the function’s return address; or explain briefly why this is impossible.

3pts Any char* string more than 40 characters long.

QUESTION ASM-22B. Which object in function _Z4buf2m is referenced using %rip -relative addressing?

3pts The string "%zu" , which is a format string passed to sprintf .

QUESTION ASM-22C. Give argument(s) to this function, including types and values, that would cause a buffer overflow that overwrote at least part of the function’s return address; or explain briefly why this is impossible.

4pts Any size_t with more than eight decimal digits, such as (size_t) -1 .

QUESTION ASM-22D. It is possible to change two lines of assembly in this function so that the revised function performs the same task, but never causes buffer overflow. Describe how.

3pts Change the two 16 offsets to 0 . No size_t has decimal length > 24.

ASM-23. Get–set interfaces

The following questions concern get–set interfaces . These are map-like data structures which support two operations:

void set( container , key , value ) Change container ’s value for key to value .

value_type get( container , key ) Returns container ’s current value for key . This is the most recent value set by set( container , key , value ) or, if there is no previous set , the natural default for the value type (0, nullptr , empty string—whatever’s appropriate).

Here’s the assembly definition of xxx1 , which is either get or set for a data structure.

QUESTION ASM-23A. Is this get or set ?

6pts for A-D. +5 1 wrong, +3 2 wrong, +2 3 wrong It is get .

QUESTION ASM-23B. What kind of data structure is this?

QUESTION ASM-23C. What can you tell about the type of key arguments for this data structure?

Unsigned 4- or 8-byte integer. Any form of “int” or “long” is full credit

QUESTION ASM-23D. What can you tell about the type of value arguments?

8 bytes big

QUESTION ASM-23E. Write a C++ version of the other operation for the same data structure, including a function signature and any type definitions required.

3pts void set (uintptr_t * a, uintptr_t k, uintptr_t v) { a[k] = v; }

Here’s the assembly definition of xxx2 , which is either get or set for a different data structure.

QUESTION ASM-23F. Is this get or set ?

2pts It is get .

QUESTION ASM-23G. Write a C++ version of the other operation for the same data structure, including a function signature and any type definitions required. You will need to call malloc or new .

4pts This is a bit of a challenge. +2 for any reasonable struct definition. Reserve +4 for people who call new at the right place and get the recursion idea. -0 if they forget to initialize the new node completely. struct node { uintptr_t key; uintptr_t value; node * child[ 2 ]; } void set (node * n, uintptr_t key, uintptr_t value) { if (n -> key == key) { n -> value = value; } else { node ** ch = & n -> child[key > n -> key]; if ( !* ch) { * ch = new node; ( * ch) -> key = key; ( * ch) -> child[ 0 ] = ( * ch) -> child[ 1 ] = nullptr ; } set( * ch, key, value); } }

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40 Basic Practices in Assembly Language Programming

• Download Loop Test Project - 34.8 Kb
• Download Calling ASM Proc In C Project - 2.9 KB
• Download Test ADDR - 4.2 KB

Introduction

1. using less instructions, 2. using an instruction with less bytes, 3. implementing with memory variables, 4. if you can use registers, don’t use memory, 5. using atomic instructions, 6. memory representations, 7. a code error hidden by little-endian, 8. assignment with push and pop is not efficient, 9. using inc to avoid pushfd and popfd, 10. another good reason to avoid push and pop, 11. implementing with plus (+) instead of add, 12. if you can use an operator, don’t use an instruction, 13. if you can use a symbolic constant, don’t use a variable, 14. generating the memory block in macro, 15. encapsulating all loop logic in the loop body, 16. loop entrance and exit, 17. don’t change ecx in the loop body, 18. when jump backward…, 19. implementing c/c++ for loop and while loop, 20. making your loop more efficient with a jump, 21. making a clear calling interface, 22. invoke vs. call, 23. call-by-value vs. call-by-reference, 24. avoid multiple ret, 25. indirect operand and lea, 26. reducing system i/o api calls, 27. defining a pointer, cast and dereference, 28. using ptr in a procedure, 29. comparison with conditional jumps, 30. when cbw, cwd, or cdq mistakenly meets div..., 31. why 255-1 and 255+(-1) affect cf differently, 32. how to determine of, 33. when local used in a procedure, 34. when local used in a macro, 35. using c calling convention in two ways, 36. using std calling convention in two ways, 37. calling cin/cout in an assembly procedure, 38. with global variables defined in data segment, 39. with local variables created in a procedure, 40. with arguments received from within a procedure.

Assembly language is a low-level programming language for niche platforms such as IoTs, device drivers, and embedded systems. Usually, it’s the sort of language that Computer Science students should cover in their coursework and rarely use in their future jobs. From TIOBE Programming Community Index , assembly language has enjoyed a steady rise in the rankings of the most popular programming languages recently.

In the early days, when an application was written in assembly language, it had to fit in a small amount of memory and run as efficiently as possible on slow processors. When memory becomes plentiful and processor speed is dramatically increased, we mainly rely on high level languages with ready made structures and libraries in development. If necessary, assembly language can be used to optimize critical sections for speed or to directly access non-portable hardware. Today assembly language still plays an important role in embedded system design, where performance efficiency is still considered as an important requirement.

In this article, we’ll talk about some basic criteria and code skills specific to assembly language programming. Also, considerations would be emphasized on execution speed and memory consumption. I'll analyze some examples, related to the concepts of register, memory, and stack, operators and constants, loops and procedures, system calls, etc.. For simplicity, all samples are in 32-bit, but most ideas will be easily applied to 64-bit.

All the materials presented here came from my teaching [1] for years. Thus, to read this article, a general understanding of Intel x86-64 assembly language is necessary, and being familiar with Visual Studio 2010 or above is assumed. Preferred, having read Kip Irvine’s textbook [2] and the MASM Programmer's Guide [3] are recommended. If you are taking an Assembly Language Programming class, this could be a supplemental reading for studies.

About instruction

The first two rules are general. If you can use less, don’t use more.

Suppose that we have a 32-bit DWORD variable:

The example is to add var1 to EAX . This is correct with MOV and ADD :

But as ADD can accept one memory operand, you can just

Suppose that we have an array:

If want to rearrange the values to be 3,1,2, you could

But notice that the last instruction should be MOV instead of XCHG . Although both can assign 3 in EAX to the first array element, the other way around in exchange XCHG is logically unnecessary.

Be aware of code size, MOV takes 5-byte machine code but XCHG takes 6, as another reason to choose MOV here:

To check machine code, you can generate a Listing file in assembling or open the Disassembly window at runtime in Visual Studio. Also, you can look up from the Intel instruction manual .

About register and memory

In this section, we’ll use a popular example, the nth Fibonacci number , to illustrate multiple solutions in assembly language. The C function would be like:

At first, let’s copy the same idea from above with two variables previous and current created here

We can use EAX store the result without the next variable. Since MOV cannot move from memory to memory, a register like EDX must be involved for assignment previous = current . The following is the procedure FibonacciByMemory . It receives n from ECX and returns EAX as the nth Fibonacci number calculated:

A basic rule in assembly language programming is that if you can use a register, don’t use a variable. The register operation is much faster than that of memory. The general purpose registers available in 32-bit are EAX , EBX , ECX , EDX , ESI , and EDI . Don’t touch ESP and EBP that are for system use.

Now let EBX replace the previous variable and EDX replace current . The following is FibonacciByRegMOV , simply with three instructions needed in the loop:

A further simplified version is to make use of XCHG which steps up the sequence without need of EDX . The following shows FibonacciByRegXCHG machine code in its Listing, where only two instructions of three machine-code bytes in the loop body:

In concurrent programming

The x86-64 instruction set provides many atomic instructions with the ability to temporarily inhibit interrupts, ensuring that the currently running process cannot be context switched, and suffices on a uniprocessor. In someway, it also would avoid the race condition in multi-tasking. These instructions can be directly used by compiler and operating system writers.

As seen above used XCHG , so called as atomic swap, is more powerful than some high level language with just one statement:

A classical way to swap a register with a memory var1 could be

Moreover, if you use the Intel486 instruction set with the .486 directive or above, simply using the atomic XADD is more concise in the Fibonacci procedure. XADD exchanges the first operand (destination) with the second operand (source), then loads the sum of the two values into the destination operand. Thus we have

Two atomic move extensions are MOVZX and MOVSX . Another worth mentioning is bit test instructions, BT , BTC , BTR , and BTS . For the following example

Imagine the instruction set without BTC , one non-atomic implementation for the same logic would be

Little-endian

An x86 processor stores and retrieves data from memory using little-endian order (low to high). The least significant byte is stored at the first memory address allocated for the data. The remaining bytes are stored in the next consecutive memory positions.

Consider the following data definitions:

For simplicity, the hexadecimal constants are used as initializer. The memory representation is as follows:

As for multiple-byte DWORD and WORD date, they are represented by the little-endian order. Based on this, the second DWORD initialized with 'AB' should be 00004142h and next '123' is 00313233h in their original order. You can't initialize dw3 as 'ABCDE' that contains five bytes 4142434445h , while you really can initialize by3 in a byte memory since no little-endian for byte data. Similarly, see w1 for a WORD memory.

From the last section of using XADD , we try to fill in a byte array with first 7 Fibonacci numbers, as 01 , 01 , 02 , 03 , 05 , 08 , 0D . The following is such a simple implementation but with a bug. The bug does not show up an error immediately because it has been hidden by little-endian.

To debug, I purposely make a memory 'ABCDEF' at the end of the byte array FibArray with seven 0ffh initialized. The initial memory looks like this:

Let's set a breakpoint in the loop. When the first number 01 filled, it is followed by three zeros as this:

But OK, the second number 01 comes to fill the second byte to overwrite three zeros left by the first. So on and so forth, until the seventh 0D , it just fits the last byte here:

All fine with an expected result in FibArray because of little-endian. Only when you define some memory immediately after this FibArray , your first three byte will be overwritten by zeros, as here 'ABCDEF' becomes 'DEF' . How to make an easy fix?

About runtime stack

The runtime stack is a memory array directly managed by the CPU, with the stack pointer register ESP holding a 32-bit offset on the stack. ESP is modified by instructions CALL , RET , PUSH , POP , etc.. When use PUSH and POP or alike, you explicitly change the stack contents. You should be very cautious without affecting other implicit use, like CALL and RET , because you programmer and the system share the same runtime stack.

In assembly code, you definitely can make use of the stack to do assignment previous = current , as in FibonacciByMemory . The following is FibonacciByStack where only difference is using PUSH and POP instead of two MOV instructions with EDX .

As you can imagine, the runtime stack built on memory is much slower than registers. If you create a test benchmark to compare above procedures in a long loop, you’ll find that FibonacciByStack is the most inefficient. My suggestion is that if you can use a register or memory, don’t use PUSH and POP .

When you use the instruction ADC or SBB to add or subtract an integer with the previous carry, you reasonably want to reserve the previous carry flag ( CF ) with PUSHFD and POPFD , since an address update with ADD will overwrite the CF . The following Extended_Add example borrowed from the textbook [2] is to calculate the sum of two extended long integers BYTE by BYTE :

As we know, the INC instruction makes an increment by 1 without affecting the CF . Obviously we can replace above ADD with INC to avoid PUSHFD and POPFD . Thus the loop is simplified like this:

Now you might ask what if to calculate the sum of two long integers DWORD by DWORD where each iteration must update the addresses by 4 bytes, as TYPE DWORD . We still can make use of INC to have such an implementation:

Applying a scaling factor here would be more general and preferred. Similarly, wherever necessary, you also can use the DEC instruction that makes a decrement by 1 without affecting the carry flag.

Since you and the system share the same stack, you should be very careful without disturbing the system use. If you forget to make PUSH and POP in pair, an error could happen, especially in a conditional jump when the procedure returns.

The following Search2DAry searches a 2-dimensional array for a value passed in EAX . If it is found, simply jump to the FOUND label returning one in EAX as true, else set EAX zero as false.

Let’s call it in main by preparing the argument ESI pointing to the array address and the search value EAX to be 31h or 30h respectively for not-found or found test case:

Unfortunately, it’s only working in not-found for 31h . A crash occurs for a successful searching like 30h , because of the stack leftover from an outer loop counter pushed. Sadly enough, that leftover being popped by RET becomes a return address to the caller.

Therefore, it’s better to use a register or variable to save the outer loop counter here. Although the logic error is still, a crash would not happen without interfering with the system. As a good exercise, you can try to fix.

Assembling time vs. runtime

I would like to talk more about this assembly language feature. Preferred, if you can do something at assembling time, don’t do it at runtime. Organizing logic in assembling indicates doing a job at static (compilation) time, not consuming runtime. Differently from high level languages, all operators in assembly language are processed in assembling such as + , - , * , and / , while only instructions work at runtime like ADD , SUB , MUL , and DIV .

Let’s redo Fibonacci calculating to implement eax = ebx + edx in assembling with the plus operator by help of the LEA instruction. The following is FibonacciByRegLEA with only one line changed from FibonacciByRegMOV .

This statement is encoded as three bytes implemented in machine code without an addition operation explicitly at runtime:

This example doesn’t make too much performance difference, compared to FibonacciByRegMOV . But is enough as an implementation demo.

For an array defined as:

If you want to traverse it from the second element to the middle one, you might think of this like in other language:

Remember that ADD , SUB , and DIV are dynamic behavior at runtime. If you know values in advance, they are unnecessary to calculate at runtime, instead, apply operators in assembling:

This saves three instructions in the code segment at runtime. Next, let’s save memory in the data segment.

Like operators, all directives are processed at assembling time. A variable consumes memory and has to be accessed at runtime. As for the last Ary1 , you may want to remember its size in byte and the number of elements like this:

It is correct but not preferred because of using two variables. Why not simply make them symbolic constants to save the memory of two DWORD ?

Using either equal sign or EQU directive is fine. The constant is just a replacement during code preprocessing.

For an amount of data to initialize, if you already know the logic how to create, you can use macro to generate memory blocks in assembling, instead of at runtime. The following macro creates all 47 Fibonacci numbers in a DWORD array named FibArray :

As macro goes to the assembler to be processed statically, this saves considerable initializations at runtime, as opposed to FibonacciByXXX mentioned before.

For more about macro in MASM, see my article Something You May Not Know About the Macro in MASM [4] . I also made a reverse engineering for the switch statement in VC++ compiler implementation. Interestingly, under some condition the switch statement chooses the binary search but without exposing the prerequisite of a sort implementation at runtime. It’s reasonable to think of the preprocessor that does the sorting with all known case values in compilation. The static sorting behavior (as opposed to dynamic behavior at runtime), could be implemented with a macro procedure, directives and operators. For details, please see Something You May Not Know About the Switch Statement in C/C++ [5] .

About loop design

Almost every language provides an unconditional jump like GOTO , but most of us rarely use it based on software engineering principles. Instead, we use others like break and continue . While in assembly language, we rely more on jumps either conditional or unconditional to make control workflow more freely. In the following sections, I list some ill-coded patterns.

To construct a loop, try to make all your loop contents in the loop body. Don’t jump out to do something and then jump back into the loop. The example here is to traverse a one-dimensional integer array. If find an odd number, increment it, else do nothing.

Two unclear solutions with the correct result would be possibly like:

However, they both do incrementing outside and then jump back. They make a check in the loop but the left does incrementing after the loop and the right does before the loop. For a simple logic, you may not think like this; while for a complicated problem, assembly language could lead astray to produce such a spaghetti pattern. The following is a good one, which encapsulates all logic in the loop body, concise, readable, maintainable, and efficient.

Usually preferred is a loop with one entrance and one exit. But if necessary, two or more conditional exits are fine as shown in Search2DAry with found and not-found results.

The following is a bad pattern of two-entrance, where one gets into START via initialization and another directly goes to MIDDLE . Such a code is pretty hard to understand. Need to reorganize or refactor the loop logic.

The following is a bad pattern of two-loop ends, where some logic gets out of the first loop end while the other exits at the second. Such a code is quite confusing. Try to reconsider with a label jumping to maintain one loop end.

The register ECX acts as a loop counter and its value is implicitly decremented when using the LOOP instruction. You can read ECX and make use of its value in iteration. As see in Search2DAry in the previous section, we compare the indirect operand [ESI+ECX-1] with AL . But never try to change the loop counter within the loop body that makes code hard to understand and hard to debug. A good practice is to think of the loop counter ECX as read-only.

Besides the LOOP instruction, assembly language programming can heavily rely on conditional or unconditional jumps to create a loop when the count is not determined before the loop. Theoretically, for a backward jump, the workflow might be considered as a loop. Assume that jx and jy are desired jump or LOOP instructions. The following backward jy L2 nested in the jx L1 is probably thought of as an inner loop.

To have selection logic of if-then-else, it's reasonable to use a foreword jump like this as branching in the jx L1 iteration:

The high level language usually provides three types of loop constructs. A FOR loop is often used when a known number of iterations available in coding that allows to initiate a loop counter as a check condition, and to change the count variable each iteration. A WHILE loop may be used when a loop counter is unknown, e.g, it might be determined by the user input as an ending flag at runtime. A DO-WHILE loop executes the loop body first and then check the condition. However, the usage is not so strictly clear and limited, since one loop can be simply replaced (implemented) by the other programmatically.

Let's see how the assembly code implements three loop structures in high level language. The previously mentioned LOOP instruction should behave like the FOR loop, because you have to initialize a known loop counter in ECX . The " LOOP target " statement takes two actions:

• decre ment ECX
• if ECX != 0 , jump to target

To calculate the sum of n+(n-1)+...+2+1 , we can have

This is the same as the FOR loop:

How about the following logic - for a WHILE loop to add any non-zero input numbers until a zero entered:

There is no meaning to use LOOP here, because you could not set or ignore any value in ECX . Instead, using a conditional jump to manually construct such a loop is required:

Here the Irvine32 library procedure ReadInt is used to read an integer from the console into EAX . Using OR instead of CMP is just for efficiency, as OR doesn't affect EAX while affecting the zero flag for JZ . Next, considering the similar logic with DO-WHILE loop:

Still with a conditional jump to have a loop here, the code looks more straight, as it does loop body first and then check:

Based on above understanding, we can now turn to the loop optimization in assembly code. For detailed instruction mechanisms, please see the Intel® 64 and IA-32 Architectures Optimization Reference Manual . Here, I only use an example of calculating the sum of n+(n-1)+...+2+1 to illustrate the performance comparison between iteration implementations of LOOP and conditional jumps. As code in the last section, I create our first procedure named as Using_LOOP :

To manually simulate the LOOP instruction, I simply decrement ECX and if not zero, go back to the loop label. So I name the second one Using_DEC_JNZ :

A similar alternative could be a third procedure by using JECXZ below, naming it as Using_DEC_JECXZ_JMP :

Now let's test three procedures by accepting a number n from the user input to save the loop counter, and then calling each procedure with a macro mCallSumProc (Here Clrscr , ReadDec , Crlf , and mWrite are from Irvine32 that will be mentioned shortly):

To test, enter a large number like 4 billion. Although the sum is far beyond the 32-bit maximum 0FFFFFFFFh , with only remainder left in EAX as (1+2+...+n) MOD 4294967295, it doesn't matter to our benchmark test. The following is the result from my Intel Core i7, 64-bit BootCamp:

Probably, the result will be slightly different on different systems. The test executable is available for try at LoopTest.EXE . Basically, using a conditional jump to construct your loop is more efficient than using the LOOP instruction directly. You can read "Intel® 64 and IA-32 Architectures Optimization Reference Manual" to find why. Also I would like to thank Mr. Daniel Pfeffer for his nice comments about optimizations that you can read in Comments and Discussions at the end.

Finally, I present above unmentioned macro as below. Again, it contains some Irvine32 library procedure calls. The source code in this section can be downloaded at Loop Test ASM Project . To understand further, please see the links in References

About procedure

Similar to functions in C/C++, we talk about some basics in assembly language's procedure.

When design a procedure, we hope to make it as reusable as possible. Make it perform only one task without others like I/O. The procedure's caller should take the responsibility to do input and putout. The caller should communicate with the procedure only by arguments and parameters. The procedure should only use parameters in its logic without referring outside definitions, without any:

• Global variable and array
• Global symbolic constant

Because implementing with such a definition makes your procedure un-reusable.

Recalling previous five FibonacciByXXX procedures, we use register ECX as both argument and parameter with the return value in EAX to make a clear calling interface:

Now the caller can do like

To illustrate as a second example, let’s take a look again at calling Search2DAry in the previous section. The register arguments ESI and EAX are prepared so that the implementation of Search2DAry doesn’t directly refer to the global array, ary2D .

Unfortunately, the weakness is its implementation still using two global constants NUM_ROW and NUM_COL that makes it not being called elsewhere. To improve, supplying other two register arguments would be an obvious way, or see the next section.

Besides the CALL instruction from Intel, MASM provides the 32-bit INVOKE directive to make a procedure call easier. For the CALL instruction, you only can use registers as argument/parameter pair in calling interface as shown above. The problem is that the number of registers is limited. All registers are global and you probably have to save registers before calling and restore after calling. The INVOKE directive gives the form of a procedure with a parameter-list, as you experienced in high level languages.

When consider Search2DAry with a parameter-list without referring the global constants NUM_ROW and NUM_COL , we can have its prototype like this

Again, as an exercise, you can try to implement this for a fix. Now you just do

Likewise, to construct a parameter-list procedure, you still need to follow the rule without referring global variables and constants. Besides, also attention to:

• The entire calling interface should only go through the parameter list without referring any register values set outside the procedure.

Also be aware of that a parameter-list should not be too long. If so, use an object parameter instead. Suppose that you fully understood the function concept, call-by-value and call-by-reference in high level languages. By learning the stack frame in assembly language, you understand more about the low-level function calling mechanism. Usually for an object argument, we prefer passing a reference, an object address, rather than the whole object copied on the stack memory.

To demonstrate this, let’s create a procedure to write month, day, and year from an object of the Win32 SYSTEMTIME structure.

The following is the version of call-by-value, where we use the dot operator to retrieve individual WORD field members from the DateTime object and extend their 16-bit values to 32-bit EAX :

The version of call-by-reference is not so straight with an object address received. Not like the arrow ->, pointer operator in C/C++, we have to save the pointer (address) value in a 32-bit register like ESI . By using ESI as an indirect operand, we must cast its memory back to the SYSTEMTIME type. Then we can get the object members with the dot:

You can watch the stack frame of argument passed for two versions at runtime. For WriteDateByVal , eight WORD members are copied on the stack and consume sixteen bytes, while for WriteDateByRef , only need four bytes as a 32-bit address. It will make a big difference for a big structure object, though.

To construct a procedure, it’s ideal to make all your logics within the procedure body. Preferred is a procedure with one entrance and one exit. Since in assembly language programming, a procedure name is directly represented by a memory address, as well as any labels. Thus directly jumping to a label or a procedure without using CALL or INVOKE would be possible. Since such an abnormal entry would be quite rare, I am not to going to mention here.

Although multiple returns are sometimes used in other language examples, I don’t encourage such a pattern in assembly code. Multiple RET instructions could make your logic not easy to understand and debug. The following code on the left is such an example in branching. Instead, on the right, we have a label QUIT at the end and jump there making a single exit, where probably do common chaos to avoid repeated code.

Object data members

Similar to above SYSTEMTIME structure, we can also create our own type or a nested:

The Rectangle type contains two COORD members, UpperLeft and LowerRight . The Win32 COORD contains two WORD ( SHORT ), X and Y . Obviously, we can access the object rect ’s data members with the dot operator from either direct or indirect operand like this

By using the OFFSET operator, we access different data member values with different type casts. Recall that any operator is processed in assembling at static time. What if we want to retrieve a data member’s address (not value) at runtime?

For an indirect operand pointing to an object, you can’t use the OFFSET operator to get the member's address, because OFFSET only can take an address of a variable defined in the data segment.

There could be a scenario that we have to pass an object reference argument to a procedure like WriteDateByRef in the previous section, but want to retrieve its member’s address (not value). Still use the above rect object for an example. The following second use of OFFSET is not valid in assembling:

Let’s ask for help from the LEA instruction that you have seen in FibonacciByRegLEA in the previous section. The LEA instruction calculates and loads the effective address of a memory operand. Similar to the OFFSET operator, except that only LEA can obtain an address calculated at runtime:

I purposely have EBX here to get an address statically and you can verify the same address in EDI that is loaded dynamically from the indirect operand ESI at runtime.

About system I/O

From Computer Memory Basics , we know that I/O operations from the operating system are quite slow. Input and output are usually in the measurement of milliseconds, compared with register and memory in nanoseconds or microseconds. To be more efficient, trying to reduce system API calls is a nice consideration. Here I mean Win32 API call. For details about the Win32 functions mentioned in the following, please refer to MSDN to understand.

An example is to output 20 lines of 50 random characters with random colors as below:

We definitely can generate one character to output a time, by using SetConsoleTextAttribute and WriteConsole . Simply set its color by

Then write that character by

When write 50 characters, make a new line. So we can create a nested iteration, the outer loop for 20 rows and the inner loop for 50 columns. As 50 by 20 , we call these two console output functions 1000 times.

However, another pair of API functions can be more efficient, by writing 50 characters in a row and setting their colors once a time. They are WriteConsoleOutputAttribute and WriteConsoleOutputCharacter . To make use of them, let’s create two procedures:

We call them in a loop to prepare a WORD array bufColor and a BYTE array bufChar for all 50 characters selected. Now we can write the 50 random characters per line with two calls here:

Besides bufColor and bufChar , we define MAXCOL = 50 and the COORD type xyPos so that xyPos.y is incremented each row in a single loop of 20 rows. Totally we only call these two APIs 20 times.

About PTR operator

MASM provides the operator PTR that is similar to the pointer * used in C/C++. The following is the PTR specification:

• type PTR expression Forces the expression to be treated as having the specified type.
• [[ distance ]] PTR type Specifies a pointer to type.

This means that two usages are available, such as BYTE PTR or PTR BYTE . Let's discuss how to use them.

The following C/C++ code demonstrates which type of Endian is used in your system, little endian or big endian? As an integer type takes four bytes, it makes a pointer type cast from the array name fourBytes , a char address, to an unsigned int address. Then it displays the integer result by dereferencing the unsigned int pointer.

As expected in x86 Intel based system, this verifies the little endian by showing 78563412 in hexadecimal. We can do the same thing in assembly language with DWORD PTR , which is just similar to an address casting to 4-byte DWORD , the unsigned int type.

There is no explicit dereference here, since DWORD PTR combines four bytes into a DWORD memory and lets MOV retrieve it as a direct operand to EAX . This could be considered equivalent to the ( unsigned int * ) cast.

Now let's do another way by using PTR DWORD . Again, with the same logic above, this time we define a DWORD pointer type first with TYPEDEF :

This could be considered equivalent to defining the pointer type as unsigned int * . Then in the following data segment, the address variable dwPtr takes over the fourBytes memory. Finally in code, EBX holds this address as an indirect operand and makes an explicit dereference here to get its DWORD value to EAX .

To summarize, PTR DWORD indicates a DWORD address type to define(declare) a variable like a pointer type. While DWORD PTR indicates the memory pointed by a DWORD address like a type cast.

To define a procedure with a parameter list, you might want to use PTR in both ways. The following is such an example to increment each element in a DWORD array:

As the first parameter pAry is a DWORD address, so PTR DWORD is used as a parameter type. In the procedure, when incrementing a value pointed by the indirect operand EDI , you must tell the system what the type(size) of that memory is by using DWORD PTR .

Another example is the earlier mentioned WriteDateByRef , where SYSTEMTIME is a Windows defined structure type.

Likewise, we use PTR SYSTEMTIME as the parameter type to define datetimePtr . When ESI receives an address from datetimePtr , it has no knowledge about the memory type just like a void pointer in C/C++. We have to cast it as a SYSTEMTIME memory, so as to retrieve its data members.

Signed and Unsigned

In assembly language programming, you can define an integer variable as either signed as SBYTE , SWORD , and SDWORD , or unsigned as BYTE , WORD , and DWORD . The data ranges, for example of 8-bit, are

• BYTE : 0 to 255 ( 00h to FFh ), totally 256 numbers
• SBYTE : half negatives, -128 to -1 ( 80h to FFh ), half positives, 0 to 127 ( 00h to 7Fh )

Based on the hardware point of view, all CPU instructions operate exactly the same on signed and unsigned integers, because the CPU cannot distinguish between signed and unsigned. For example, when define

Both of them have the 8-bit binary FFh saved in memory or moved to a register. You, as a programmer, are solely responsible for using the correct data type with an instruction and are able to explain a results from the flags affected:

• The carry flag CF for unsigned integers
• The overflow flag OF for signed integers

The following are usually several tricks or pitfalls.

Let's check the following code to see which label it jumps:

As we know, CMP follows the same logic as SUB while non-destructive to the destination operand. Using JA means considering unsigned comparison, where the destination EAX is FFh , i.e. 255 , while the source is 1 . Certainly 255 is bigger than 1 , so that makes it jump to L1 . Thus, any unsigned comparisons such as JA , JB , JAE , JNA , etc. can be remembered as A(Above) or B(Below). An unsigned comparison is determined by CF and the zero flag ZF as shown in the following examples:

Now let's take a look at signed comparison with the following code to see where it jumps:

Only difference is JG here instead of JA . Using JG means considering signed comparison, where the destination EAX is FFh , i.e. -1 , while the source is 1 . Certainly -1 is smaller than 1 , so that makes JMP to L2 . Likewise, any signed comparisons such as JG , JL , JGE , JNG , etc. can be thought of as G(Greater) or L(Less). A signed comparison is determined by OF and the sign flag SF as shown in the following examples:

As we know, the DIV instruction is for unsigned to perform 8-bit, 16-bit, or 32-bit integer division with the dividend AX , DX:AX , or EDX:EAX respectively. As for unsigned, you have to clear the upper half by zeroing AH , DX , or EDX before using DIV . But when perform signed division with IDIV , the sign extension CBW , CWD , and CDQ are provided to extend the upper half before using IDIV .

For a positive integer, if its highest bit (sign bit) is zero, there is no difference to manually clear the upper part of a dividend or mistakenly use a sign extension as shown in the following example:

This is fine because 1000h is a small positive and CDQ makes EDX zero, the same as directly clearing EDX . So if your value is positive and its highest bit is zero, using CDQ and

are exactly the same.

However, it doesn’t mean that you can always use CDQ / CWD / CBW with DIV when perform a positive division. For an example of 8-bit, 129/2 , expecting quotient 64 and remainder 1 . But, if you make this

Try above in debug to see how integer division overflow happens as a result. If really want to make it correct as unsigned DIV , you must:

On the other side, if really want to use CBW , it means that you perform a signed division. Then you must use IDIV :

As seen here, 81h in signed byte is decimal -127 so that signed IDIV gives the correct quotient and remainder as above

To talk about the carry flag CF , let's take the following two arithmetic calculations:

From a human being's point of view, they do exactly the same operation, 255 minus 1 with the result 254 ( FEh ). Likewise, based on the hardware point, for either calculation, the CPU does the same operation by representing -1 as a two's complement FFh and then add it to 255 . Now 255 is FFh and the binary format of -1 is also FFh . This is how it has been calculated:

Remember? A CPU operates exactly the same on signed and unsigned because it cannot distinguish them. A programmer should be able to explain the behavior by the flag affected. Since we talk about the CF , it means we consider two calculations as unsigned. The key information is that -1 is FFh and then 255 in decimal. So the logic interpretation of CF is

• For sub al, 1 , it means 255 minus 1 to result in 254 , without need of a borrow, so CF = 0
• For add bl, -1 , it seems that 255 plus 255 is resulted in 510 , but with a carry 1,0000,0000b ( 256 ) out, 254 is a remainder left in byte, so CF = 1

From hardware implementation, CF depends on which instruction used, ADD or SUB . Here MSB (Most Significant Bit) is the highest bit.

• For ADD instruction, add bl, -1 , directly use the carry out of the MSB, so CF = 1
• For SUB instruction, sub al, 1 , must INVERT the carry out of the MSB, so CF = 0

Now let's see the overflow flag OF , still with above two arithmetic calculations as this:

Both of them are not overflow, so OF = 0 . We can have two ways to determine OF , the logic rule and hardware implementation.

Logic viewpoint : The overflow flag is only set, OF = 1 , when

• Two positive operands are added and their sum is negative
• Two negative operands are added and their sum is positive

For signed, 255 is -1 ( FFh ). The flag OF doesn't care about ADD or SUB . Our two examples just do -1 plus -1 with the result -2 . Thus, two negatives are added with the sum still negative, so OF = 0 .

Hardware implementation : For non-zero operands,

• OF = (carry out of the MSB) XOR (carry into the MSB)

As seen our calculation again:

The carry out of the MSB is 1 and the carry into the MSB is also 1 . Then OF = ( 1 XOR 1 ) = 0

To practice more, the following table enumerates different test cases for your understanding:

Ambiguous "LOCAL" directive

As mentioned previously, the PTR operator has two usages such as DWORD PTR and PTR DWORD . But MASM provides another confused directive LOCAL , that is ambiguous depending on the context, where to use with exactly the same reserved word. The following is the specification from MSDN :

        LOCAL localname [[, localname]]...         LOCAL label [[ [count ] ]] [[:type]] [[, label [[ [count] ]] [[type]]]]...

• In the first directive, within a macro, LOCAL defines labels that are unique to each instance of the macro.
• In the second directive, within a procedure definition (PROC), LOCAL creates stack-based variables that exist for the duration of the procedure. The label may be a simple variable or an array containing count elements.

This specification is not clear enough to understand. In this section, I'll expose the essential difference in between and show two example using the LOCAL directive, one in a procedure and the other in a macro. As for your familiarity, both examples calculate the nth Fibonacci number as early FibonacciByMemory . The main point delivered here is:

• The variables declared by LOCAL in a macro are NOT local to the macro. They are system generated global variables on the data segment to resolve redefinition.
• The variables created by LOCAL in a procedure are really local variables allocated on the stack frame with the lifecycle only during the procedure.

For the basic concepts and implementations of data segment and stack frame , please take a look at some textbook or MASM manual that could be worthy of several chapters without being talked here.

The following is a procedure with a parameter n to calculate nth Fibonacci number returned in EAX . I let the loop counter ECX take over the parameter n . Please compare it with FibonacciByMemory . The logic is the same with only difference of using the local variables pre and cur here, instead of global variables previous and current in FibonacciByMemory .

The following is the code generated from the VS Disassembly window at runtime. As you can see, each line of assembly source is translated into machine code with the parameter n and two local variables created on the stack frame, referenced by EBP :

When FibonacciByLocalVariable running, the stack frame can be seen as below:

Obviously, the parameter n is at EBP+8 . This

moving the stack pointer ESP down eight bytes for two DWORD creation of pre and cur . Finally the LEAVE instruction implicitly does

that moves EBP back to ESP releasing the local variables pre and cur . And this releases n , at EBP+8 , for STD calling convention:

To have a macro implementation, I almost copy the same code from FibonacciByLocalVariable . Since no USES for a macro, I manually use PUSH / POP for ECX and EDX . Also without a stack frame, I have to create global variables mPre and mCur on the data segment. The mFibonacciByMacro can be like this:

If you just want to call mFibonacciByMacro once, for example

You don't need LOCAL here. Let's simply comment it out:

mFibonacciByMacro accepts the argument 12 and replace n with 12 . This works fine with the following Listing MASM generated:

Nothing changed from the original code with just a substitution of 12 . The variables mPre and mCur are visible explicitly. Now let's call it twice, like

This is still fine for the first mFibonacciByMacro 12 but secondly, causes three redefinitions in preprocessing mFibonacciByMacro 13 . Not only are data labels, i.e., variables mPre and mCur , but also complained is the code label mL . This is because in assembly code, each label is actually a memory address and the second label of any mPre , mCur , or mL should take another memory, rather than defining an already created one:

To rescue, let's turn on this:

Again, running mFibonacciByMacro twice with 12 and 13 , fine this time, we have:

Now the label names, mPre , mCur , and mL , are not visible. Instead, running the first of mFibonacciByMacro 12 , the preprocessor generates three system labels ??0000 , ??0001 , and ??0002 for mPre , mCur , and mL . And for the second mFibonacciByMacro 13 , we can find another three system generated labels ??0003 , ??0004 , and ??0005 for mPre , mCur , and mL . In this way, MASM resolves the redefinition issue in multiple macro executions. You must declare your labels with the LOCAL directive in a macro.

However, by the name LOCAL , the directive sounds misleading, because the system generated ??0000 , ??0001 , etc. are not limited to a macro's context. They are really global in scope. To verify, I purposely initialize mPre and mCur as 2 and 3 :

Then simply try to retrieve the values from ??0000 and ??0001 even before calling two mFibonacciByMacro in code

To your surprise probably, when set a breakpoint, you can enter & ??0000 into the VS debug Address box as a normal variable. As we can see here, the ??0000 memory address is 0x0116518C with DWORD values 2 , 3 , and so on. Such a ??0000 is allocated on the data segment together with other properly named variables, as shown string ASCII beside:

To summarize, the LOCAL directive declared in a macro is to prevent data/code labels from being globally redefined.

Further, as an interesting test question, think of the following multiple running of mFibonacciByMacro which is working fine without need of a LOCAL directive in mFibonacciByMacro . Why?

Calling an assembly procedure in C/C++ and vice versa

Most assembly programming courses should mention an interesting topic of mixed language programming, e.g., how C/C++ code calls an assembly procedure and how assembly code calls a C/C++ function. But probably, not too much would be involved, especially for manual stack frame manipulation and name decoration. Here in first two sections, I'll give a simple example of C/C++ code calling an assembly procedure. I'll show C and STD calling conventions, using procedures either with advanced parameter lists or directly dealing with stack frame and name mangling.

The logic just calculates x-y , like 10-3 to show 7 resulted:

When calling an assembly procedure from a C/C++ function, both must be consistent to use the same calling and naming conventions, so that a linker can resolve references to the caller and its callee. As for Visual C/C++ functions, C calling convention can be designated by the keyword __cdecl that should be default in a C/C++ module. And STD calling convention can be designated by __stdcall . While on the assembly language side, MASM also provides reserved words C and stdcall correspondingly. In an assembly language module, you can simply use the .model directive to declare all procedures follow C calling convention like this:

But you also can override this global declaration by indicating an individual procedure as a different calling convention like:

The following sections suppose that you have basic knowledge and understanding about above.

Let's first see a high level procedure with a parameter list easily from the following. I purposely leave blank for the calling convention attribute field in the .model directive, but I have PROC C to define it as C calling convention:

The procedure ProcC_CallWithParameterList simply does subtraction x-y and returns the difference in EAX . In order to call it from a function in a .CPP file, I must have an equivalent C prototype declared in the .CPP file accordingly, where __cdecl is default:

Then call it in main() like

Using the language attribute C to declare ProcC_CallWithParameterList makes a lot hidden behind the scene. Please recall what happens to the C calling convention __cdecl . The main point I want show here is

Based on these specifications, I can manually create this procedure to fit C calling convention:

As seen here, an underscore is prepended as _ProcC_CallWithStackFrame and two arguments x and y passed in reverse order with the stack frame looks like this:

Now let's verify that two procedures work exactly the same by C++ calls

Now we can take a look at STD call in the similar way. The following is simply a parameter list procedure with the language attribute stdcall defined for PROC :

Except for the calling conventions, no difference between ProcSTD_CallWithParameterList and ProcC_CallWithParameterList . In order to call ProcSTD_CallWithParameterList from a C function, the prototype should be like this:

Notice that __stdcall is a must to declare this time. Likewise, using stdcall to declare ProcSTD_CallWithParameterList also hides a lot details. Please recall what happens to the STD calling convention __stdcall . The main point to talk is

Based on these specifications, I can manually create this procedure to fit STD calling convention.

Although the stack frame is the same with two arguments x and y passed in reverse order, one difference is _ProcSTD_CallWithStackFrame@8 suffixed by the number eight, 8 bytes of two int type arguments. Another is ret 8 that is for this procedure itself to release the stack argument memory.

Now put all together, we can verify four procedures getting called by C++ with the same results:

This section will answer an opposite question, how to call C/C++ functions from an assembly procedure. We really need such a technique to make use of ready-made high level language subroutines for I/O, floating point data, and math function processing. Here I simply want to perform a subtraction task in an assembly procedure, together with input and output by calling cin and cout like this:

I use C calling convention for both calls and in order to do this, let's make three C prototypes:

It's trivial defining first two functions to be called in DoSubtraction , while DoSubtraction is supposed to call in main() :

Now is time to implement the assembly procedure DoSubtraction . Since DoSubtraction will call two C++ functions for I/O, I have to make their equivalent prototypes acceptable and recognized by DoSubtraction :

Next, simply fill the logic to make it work by invoking ReadFromConsole and DisplayToConsole :

Finally, all source code in above three sections is available for download at CallingAsmProcInC , with main.cpp , subProcs.asm , and VS project.

About ADDR operator

In 32-bit mode, the INVOKE , PROC , and PROTO directives provide powerful ways for defining and calling procedures. Along with these directives, the ADDR operator is an essential helper for defining procedure parameters. By using INVOKE , you can make a procedure call almost the same as a function call in high-level programming languages, without caring about the underlying mechanism of the runtime stack.

Unfortunately, the ADDR operator is not well explained or documented. The MASM simply said it as an address expression (an expression preceded by ADDR) . The textbook [1] , mentioned a little more here:

The ADDR operator, also available in 32-bit mode, can be used to pass a pointer argument when calling a procedure using INVOKE . The following INVOKE statement, for example, passes the address of myArray to the FillArray procedure:

The argument passed to ADDR must be an assembly time constant. The following is an error:

The ADDR operator can only be used in conjunction with INVOKE . The following is an error:

All these sound fine, but are not very clear or accurate, and even not conceptually understandable in programming. ADDR not only can be used at assembly time with a global variable like myArray to replace OFFSET , it also can be placed before a stack memory, such as a local variable or a procedure parameter. The following is actually possible without causing an assembly error:

Don't do this, just because unnecessary and somewhat meaningless. The INVOKE directive automatically generates the prologue and epilogue code for you with EBP and pushes arguments in the format of EBP offset. The following sections show you how smart is the ADDR operator, with different interpretations at assembly time and at runtime.

Let's first create a procedure to perform subtraction C=A-B , with all three address parameters (call-by-reference). Obviously, we have to use indirect operand ESI and dereference it to receive two values from parA and parB . The out parameter parC saves the result back to the caller:

And define three global variables in the DATA segment:

Then directly pass these global variables to SubWithADDR with ADDR as three addresses:

Now let's generate the code Listing by use the option " Listing All Available Information " as below:

The Listing simply shows three ADDR operators replaced by OFFSET :

This is logically reasonable, since valA , valB , and valC are created statically at assembly time and the OFFSET operator must be applied at assembly time accordingly. In such a case, where we can use ADDR , we also can use OFFSET instead. Let's try

and regenerate the Listing here to see actually no essential differences:

In order to test ADDR applied to a local variable, we have to create another procedure where three local variables are defined:

Notice that locA , locB , and locC are the memory of BYTE type. To reuse SubWithADDR by INVOKE , I need to prepare values like 8 and 2 to the input arguments locA and locB , and let locC to get back the result. I have to apply ADDR to three of them to satisfy the calling interface of SubWithADDR prototype. Now simply do the second test:

At this moment, the local variables are created on the stack frame. This is the memory dynamically created at runtime. Obviously, the assembly time operator OFFSET cannot be assumed by ADDR . As you might think, the instruction LEA should be coming on duty ( LEA mentioned already: 11 . Implementing with plus (+) instead of ADD and 21 . Making a clear calling interface ).

Wow exactly, the operator ADDR is now cleaver enough to choose LEA this time. To be readable, I want to avoid using Listing to see 2s complement offset to EBP . Instead, check the Disassembly intuitive display at runtime here. The code shows three ADDR operators replaced by three LEA instructions, working with EBP on the stack as follows:

where the hexadecimal 00401030 is SubWithADDR 's address. Because of the LOCAL directive, MASM automatically generates the prologue and epilogue with EBP representations. To view EBP offset instead of variable names like locA , locB , and locC , just uncheck the Option: Show symbol names :

The third test is to make ADDR apply to arguments. I create a procedure WithArgumentPassed and call it like:

Reuse the global valC here with OFFSET , since I hope to get the result 8 back. It's interesting to see how to push three values in the Listing:

The implementation of WithArgumentPassed is quite straight and simply reuse SubWithADDR by passing arguments argA and argB prefixed with ADDR to be addresses, while ptrC already a pointer without ADDR :

If you are familiar with the concepts of stack frame, imagine the behavior of ADDR that must be very similar to the local variables, since arguments are also dynamically created memory on the stack at runtime. The following is the generated Listing with two ADDR operators replaced by LEA . Only difference is the positive offset to EBP here:

Because of WithArgumentPassed PROC with a parameter-list, MASM also generates the prologue and epilogue with EBP representations automatically. Three address arguments pushed in the reverse order are EBP plus 16 ( ptrC ), plus 12 ( argB ), and plus 8 ( argA ).

Finally, all source code in above three sections available to download at TestADDR , with TestADDR.asm , TestADDR.lst , and TestADDR.vcxproj .

I talked so much about miscellaneous features in assembly language programming. Most of them are from our class teaching and assignment discussion [1] . The basic practices are presented here with short code snippets for better understanding without irrelevant details involved. The main purpose is to show assembly language specific ideas and methods with more strength than other languages.

As noticed, I haven’t given a complete test code that requires a programming environment with input and output. For an easy try, you can go [2] to download the Irvine32 library and setup your MASM programming environment with Visual Studio, while you have to learn a lot in advance to prepare yourself first. For example, the statement exit mentioned here in main is not an element in assembly language, but is defined as INVOKE ExitProcess,0 there.

Assembly language is notable for its one-to-one correspondence between an instruction and its machine code as shown in several Listings here. Via assembly code, you can get closer to the heart of the machine, such as registers and memory. Assembly language programming often plays an important role in both academic study and industry development. I hope this article could serve as an useful reference for students and professionals as well.

• CSCI 241, Assembly Language Programming class site
• Kip Irvine, Assembly Language for x86 Processors, 7th edition
• MASM Programmer's Guide, MASM 6.1 Documentation
• Zuoliu Ding, Something You May Not Know About the Macro in MASM
• Zuoliu Ding, Something You May Not Know About the Switch Statement in C/C++
• January 28, 2019 -- Added: About ADDR operator, three sections
• January 22, 2017 -- Added: Calling an assembly procedure in C/C++ and vice versa, three sections
• January 11, 2017 -- Added: FOR/WHILE loop and Making loop more efficient, two sections
• December 20, 2016 -- Added: Ambiguous "LOCAL" directive, two sections
• November 28, 2016 -- Added: Signed and Unsigned, four sections
• October 30, 2016 -- Added: About PTR operator, two sections
• October 16, 2016 -- Added: Little-endian, two sections
• October 11, 2016 -- Added: the section, Using INC to avoid PUSHFD and POPFD
• October 2, 2016 -- Added: the section, Using atomic instructions
• August 1, 2016 -- Original version posted

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Layout   Per page     First Prev 30-Apr-20 20:07 30-Apr-20 20:07  hello can you give me full this assignment write a program to implement a 2 D array in assembly with (5 X 5) size. Hint: (1) Its matter of observation and manipulation of(indexes) (2) If row size is 5. It will start from 0 and end at 4 (3) Assume the starting relative address is 0150 Question NO# 2 Write a program that is menu driven. The program takes an input from the user until it input’ % ‘Sign. After getting input from the user the program displays a menu. Giving following options: 1) Converts the input to upper case. [2.5] 2) Search the char. Example: “Hello” user input “e “Output e is found at index ‘1’if char is found 2 time all the indexes are shown. [5] 3) Calculate the total occurrence of the letter. [5] 4) Bonus part sort the string. [5] 5) Reverse the array. [2.5] Special instruction: Need to use indirect addressing. Every option should be implemented as procedure. Use Stack and arrays where needed. Make effective use of EBP and Other register. ·   16-Dec-19 14:45 16-Dec-19 14:45  I note that you use XCHG quite frequently .. unfortunately there is a hidden "penalty" in the use of XCHG ....The sort of error that one would expect from someone unfamiliar with assembler. Perhaps you would care to look at the definition and think again. Heres a clue .. you can use XCHG in a crude [but definitely not advisable way ] to halt a threading process .. why might this be ???? its ALL in the description .. ·   4-Mar-19 10:13 4-Mar-19 10:13  I am working on something, but there is an error. Can you please try to find it. commands: ; nasm -f elf -g -F stabs evil.asm ; ld -o evil evil.o section .data Snippet: db "@E9>06G@Q:CN3C57I<)<)*" SnipLen: equ $-Snippet section .text global _start _start: nop mov ecx,Snippet mov edx,SnipLen mov eax,6 DoMore: add byte [ecx],af inc ecx inc eax dec edx jnz DoMore mov eax,4 mov ebx,1 sub ecx,SnipLen mov edx,SnipLen int 80H mov eax,1 mov ebx,0 int 80H nop ·   30-Apr-20 20:10 30-Apr-20 20:10  can you help me to solve problems? ·   31-Jan-19 8:25 31-Jan-19 8:25  In your second example: mov eax,array ; eax =1 xchg eax,[array+4] ; 1,1,3, eax =2 xchg eax,[array+8] ; 1,1,2, eax =3 xchg array,eax ; 3,1,2, eax =1 The first and last lines should read mov eax,[array+0] ; eax =1 and xchg eax,[array+0] ; 3,1,2, eax =1 (or use mov [array+0],eax as indicated in the article) Reason: Making it clear to anyone maintaining your code that these instructions are operating on an element of the array. In general all hard-coded accesses to the zeroth element of an array should take that form. A good assembler will generate the same code as your text. I am still reading your article so apologies if you have already covered this further down the page. IanS ---- Afterthought: I am very rusty with MASM, but doesn't the [] idiom act as addition? The clearer form of [foo+2] would then be foo[2], much more representative of a subscript in many computer languages. IanS -- modified 1-Feb-19 5:15am. ·   2-Feb-19 7:54 2-Feb-19 7:54  Thanks for your question. Yes, [foo+2] is the same as foo[2] This is called "Direct-Offset Operands" A constant offset is added to a data label to produce an effective address (EA). The address is dereferenced to get the value inside its memory location. where the square brackets are optional: .data arrayB BYTE 10h,20h,30h,40h .code mov al,arrayB+1 ; AL = 20h mov al,[arrayB+1] ; alternative notation So the example also can be like: mov eax,array ; eax =1 xchg eax,array[4] ; 1,1,3, eax =2 xchg eax,array+8 ; 1,1,2, eax =3 xchg array,eax ; 3,1,2, eax =1 The format could be more flexible like: xchg eax,8[array] ; 1,1,2, eax =3 xchg eax,8+array ; 1,1,2, eax =3 xchg eax,[8+array] ; 1,1,2, eax =3 All these are equivalent to array+8 or array[8] Try to verify all working the same, nice learning ASM! ·   30-Jan-19 7:02 30-Jan-19 7:02  Great article! I vote 5. A second part could be 64 bits assembly and mixed programming using fastcall ·   30-Jan-19 10:52 30-Jan-19 10:52  Thanks for your interest and suggestion. I'll try ·   27-Mar-17 6:33 27-Mar-17 6:33  Something weird is going on. I see the title on the web page, author's photo, etc., all as usual, but there is no article! Using the same computer and browser that I've always used to read Code Project posts. ·   27-Jan-17 14:28 27-Jan-17 14:28  Fantastic, Thank you. ·   21-Dec-16 10:07 21-Dec-16 10:07  Excellent! Keep up the good work ·   24-Jan-17 7:00 24-Jan-17 7:00  Thank you for your interest and encoragement. Happy New Year! ·   21-Dec-16 8:01 21-Dec-16 8:01  This is instantly one of the best developer resources for information on the internet at this time. Thank you. ·   21-Dec-16 2:18 21-Dec-16 2:18  In your example for avoiding you use the instruction, as it does not affect the carry flag. This is an excellent observation, however does affect other flags, and the instruction can only increment the operand by one. I think it would be useful to note that the instruction can be used to perform some non-flag setting arithmetic, as this instruction does not affect flags. It is quite a versatile instruction for arithmetic as well, as it can add constants to registers, perform some basic multiplication and even perform a 3-address register/register add. ·   21-Dec-16 6:13 21-Dec-16 6:13  Nice comments about LEA that really could be a smart consideration if necessary Thank you, Tom! ·   20-Dec-16 19:56 20-Dec-16 19:56  Thanks 4 Share!!!!! ·   20-Dec-16 13:02 20-Dec-16 13:02  My 5 for the article. Only two tiny things to say now: I think you have written your last change in the wrong section (References instead of History). In my opinion it will be nicer if you write the history from new to old instead of old to new (I mean newest first) ·   20-Dec-16 18:40 20-Dec-16 18:40  Hi Nelek, Thank you very much for your interest and reading so carefully to point out such a mistake. I corrected and updated now. Enjoy reading your mottos attached, ·   21-Dec-16 1:23 21-Dec-16 1:23  You are welcome ·   3-Dec-16 20:37 3-Dec-16 20:37  ·   30-Nov-16 22:25 30-Nov-16 22:25  A decent review of classical x86 assembly-language optimizations. However... [ ] ·   1-Dec-16 6:54 1-Dec-16 6:54  Hi Daniel, Yes, I totally agree. It's true that this article is far from enough for some good topics such as optimizations, modern processors, and advanced instructions. The main material was just based on the MASM 6.1 manual dated 1992. As for a primary academic purpose, our course outline is quite limited and actually lag behind the industry point of view and recent development. I believe your comment is a necessary and appropriate note here. Thank you so much, Ding ·   23-Jan-17 23:22 23-Jan-17 23:22  A superb article and brings back so many memories of times when Assembler was my bread and butter. I don't think there are limits here. Yes, it is based on classical x86 and it should be. Once learned, modern processor specific optimizations and system architecture necessities can be investigated at a later date. It is sad that probably 90% or more of "programmers" today would not have the foggiest idea of Assembly language coding even if it slapped them on the face Tom and Jerry style. ·   26-Mar-21 16:35 26-Mar-21 16:35  Thanks for your nice comment "Most modern Intel/AMD processors support SIMD instructions (MMX/SSE/AVX), which make many operations much more efficient ..." Finally I got chance to write at [ ] Best, ·   29-Nov-16 9:00 29-Nov-16 9:00  What compiler are you using for this assembly language? ·   Last Visit: 31-Dec-99 18:00     Last Update: 30-Aug-24 19:27 Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages. Themes for Morning Assembly in Schools Captivating Morning Assembly Themes to Inspire and Engage School Students Themes for Morning Assembly in Schools: Morning assemblies are the heartbeat of a school’s daily routine. Assemblies with messages that resonate with students and staff alike. By incorporating themed morning assemblies, schools can transform these gatherings into powerful conduits for inspiration, engagement, and learning. But how can one curate themes that not only captivate but also educate? Exploring the Power of Themed Morning Assemblies The significance of themed morning assemblies is undeniable. They stand as a daily ritual where the school community can unite, reflect, and prepare for the day ahead. Impactful themed assemblies foster student engagement, becoming a catalyst for personal growth and academic excellence. They are a strategic platform for promoting school culture and values , allowing students to explore various topics in an immersive and structured way. Themes for Academic Excellence and Personal Growth School Morning Assembly Themes details read below Here are some best theme ideas for morning assemblies in schools: Cultural Diversity Week: Celebrate the various cultures represented in the student body. Environmental Stewardship: Focus on green practices and appreciation for nature. Mindfulness and Meditation: Teach and practice mindfulness techniques for stress reduction. Historical Milestones: Commemorate significant events in history relevant to the students. Literary Greats: Dedicate assemblies to exploring the works of significant authors or poets. Science and Innovation: Highlight scientific discoveries and encourage innovative thinking. Art and Music Appreciation: Introduce students to various art forms and music genres. Health and Wellness: Address physical and mental health topics. Community Heroes: Honor local community leaders and unsung heroes. Global Awareness: Educate about global issues and international events. Sportsmanship and Teamwork: Emphasize the importance of fair play and working together. Digital Citizenship: Teach responsible and safe conduct in the digital world. Space Exploration: Discuss past, present, and future space missions and discoveries. Kindness Week: Encourage acts of kindness and compassion among students. Career Insights: Introduce various professions and what they entail. Language and Linguistics: Explore the beauty and complexity of different languages. Mathematics in Real Life: Show how math is used in everyday situations and careers. Theater and Performance: Promote drama and performance arts. Historic Leaders: Discuss the contributions of notable leaders from various fields. Social Media Literacy: Discuss the influence and impact of social media on society. These themes can help create a varied and engaging schedule of assemblies that are both educational and inspiring. Nurturing Academic Excellence Theme for Morning Assembly Cultivating a Growth Mindset and Embracing Challenges: A theme that inspires students to perceive challenges as opportunities for growth. Developing Effective Study Habits and Time Management Skills: Sessions focused on strategies for academic success. Celebrating Academic Achievements and Recognizing Potential: Assemblies that honor student successes, large and small, fostering an environment of encouragement. Promoting Personal Growth Theme for School Assembly Cultivating Self-Confidence and Self-Awareness: Activities that help students explore their own strengths and weaknesses. Fostering Empathy and Building Healthy Relationships: Dialogues about respect, understanding, and compassion. Embracing Diversity and Promoting Inclusivity: Programs that celebrate the myriad cultures and identities within the school community. Themes for Social Responsibility and Global Awareness Inspiring social responsibility theme for inspirational assembly. Encouraging Volunteerism and Civic Engagement: Initiatives that inspire students to give back to their communities. Promoting Social Awareness and Cultural Sensitivity: Assemblies that broaden students’ perspectives on societal issues. Addressing Global Issues and Inspiring Positive Change: Discussions that empower students to become proactive global citizens. Expanding Global Awareness for Creative Assembly Themes for Schools Celebrating Cultural Diversity and Embracing Global Perspectives: Exposing students to the wider world through cultural exploration. Exploring Environmental Issues and Promoting Sustainable Practices: Educating on the importance of environmental stewardship. Encouraging Intercultural Understanding and Global Citizenship: Assemblies that build awareness of and respect for global cultures. Themes for Mental Well-being and Creativity Nurturing mental well-being theme school assemblies. Promoting Mental Health Awareness and Stress Management: Talks and activities that address mental well-being. Cultivating Emotional Intelligence and Resilience: Helping students navigate their emotions and develop coping strategies. Recognizing Signs of Mental Health Issues and Seeking Help: Assemblies that destigmatize mental health and encourage seeking assistance. Unleashing Creativity and Innovation Theme for Daily School Assembly Concepts Fostering a Growth Environment for Creativity and Innovation: Celebrating creativity in all its forms. Encouraging Out-of-the-Box Thinking and Problem-solving: Engaging students in creative problem-solving exercises. Celebrating Creativity in Various Forms and Expressions: Showcasing student art, writing, and other creative projects. Additional Theme Suggestions for Daily School Assemblies Celebrating Cultural and Historical Heritage: Connect students to their roots and the world’s rich tapestry of history. Promoting Physical Fitness and Healthy Habits: Incorporate themes that encourage active lifestyles. Encouraging Anti-bullying and Conflict Resolution: Foster a safe and nurturing school environment. Inspiring Leadership and Teamwork Skills: Equip students with the skills to lead and collaborate effectively. Promoting Digital Literacy and Responsible Technology Use: Prepare students for a digitally-driven world. Tips for Selecting and Implementing Morning Assembly Themes When selecting engaging and universal morning assembly themes , always align with student interests, current events, and the core values of your school. Strive to make them age-appropriate and diverse , reflecting the multifaceted world we live in. Use a mix of formats—from guest speakers to interactive activities—to cater to different learning styles and keep students invested. And above all, invite student participation and feedback to ensure these assemblies resonate with their needs and interests. The transformative power of themed morning assemblies should never be underestimated. They are not just a start to the academic day but a foundation for lifelong learning and character-building. As we strive to implement inspirational and engaging morning assembly themes , let’s remember that each theme carries the potential to ignite a spark within our students, prompting them to think, question, and aspire. Additional Tips Keep your assembly concise and focused —attention spans are limited. Enhance engagement with visuals and multimedia ; they speak louder than words. Encourage a sense of unity and promote school spirit through collective themes. End each assembly on a high note, leaving students with a positive and motivating message that will resonate throughout their day. Morning assemblies are more than a tradition; they are a daily opportunity for enrichment and connection. Embrace this chance to spark curiosity, foster empathy, and encourage growth in every student that gathers in the shared space of learning and camaraderie. Daily School Morning Assembly Material for Students Paragraph on Morning Assembly in My School Morning Assembly for New Session in School The Importance of a Morning Assembly Script in Schools Assembly Topics For School: Engaging and Moral Speech Ideas Related posts: 2 thoughts on “Themes for Morning Assembly in Schools” Pingback: How to Get Students Involved in a Morning Assembly? Pingback: How to Introduce Yourself in a Morning Assembly? Leave a Comment Cancel reply Save my name, email, and website in this browser for the next time I comment. AI Community L&D On-Demand From Hurdles to Success: Navigating Troubleshooting Assembly Issues Jamie Smith Assembly Instructions: A Key to Success When it comes to successful assembly processes, clear and accurate assembly instructions play a crucial role. They serve as a guide for individuals involved in the assembly process, ensuring that each step is performed correctly and efficiently. In this section, we will explore the importance of clear and accurate assembly instructions, common challenges faced during the assembly process, and the role of troubleshooting in assembly. The Importance of Clear and Accurate Assembly Instructions Clear and accurate assembly instructions are essential for several reasons. They provide a standardized method for assembling products, ensuring consistency and quality across different assembly processes. By following well-documented instructions, assembly personnel can minimize errors and maintain productivity levels. Furthermore, clear assembly instructions contribute to a smoother workflow, reducing the need for constant supervision and intervention. They empower assembly personnel to take ownership of their work and make informed decisions during the assembly process. To create effective assembly instructions, it is crucial to consider the target audience and their level of expertise. Instructions should be written in a clear and concise manner, using simple language and avoiding technical jargon. Visual aids, such as diagrams or step-by-step assembly guides , can also enhance comprehension and facilitate the assembly process. Common Challenges in the Assembly Process The assembly process often comes with its fair share of challenges. Some common issues encountered include missing or incomplete assembly instructions, ambiguous steps, and inadequate training of assembly personnel. These challenges can lead to errors, delays, and decreased productivity. To address these challenges, it is essential to invest time and effort into developing comprehensive assembly instructions. Instructions should be reviewed and tested to ensure their accuracy and usability. Regular training sessions for assembly personnel can also help familiarize them with the assembly process and minimize errors. The Role of Troubleshooting in Assembly Troubleshooting plays a vital role in the assembly process. It involves identifying and resolving issues that arise during assembly, ensuring that the final product meets the required specifications. Effective troubleshooting can prevent defects, minimize rework, and improve overall assembly efficiency. When troubleshooting assembly issues, it is crucial to follow a systematic approach. This includes identifying the problem, analyzing the root cause, and implementing appropriate solutions. By utilizing available resources, such as effective assembly instructions and expert knowledge within the team, you can address assembly issues efficiently. By recognizing the importance of clear and accurate assembly instructions, being aware of common challenges, and understanding the role of troubleshooting, you can maximize the efficiency and quality of your assembly processes. Continuous improvement in assembly instructions, as well as regular feedback and iteration, can further enhance assembly operations. For more insights on optimizing your assembly processes, check out our article on optimizing assembly processes . Troubleshooting Assembly Issues When faced with assembly issues, it’s important to have a systematic approach to identify and resolve problems efficiently. Troubleshooting assembly issues involves three key steps: identifying the problem, analyzing the root cause, and implementing solutions. Identifying the Problem The first step in troubleshooting assembly issues is to identify the specific problem or challenge you are facing. This requires careful observation and analysis of the assembly process. Common assembly issues may include misalignment, faulty components, incomplete connections, or difficulties with specific steps. To identify the problem, examine the final output and compare it to the expected result. Look for any deviations, inconsistencies, or errors that may have occurred during the assembly. Pay attention to any warning signs, such as unusual sounds, resistance, or visual cues that indicate a potential issue. Analyzing the Root Cause After identifying the problem, the next step is to analyze the root cause. This involves investigating the underlying factors that led to the assembly issue. Analyzing the root cause helps prevent similar issues from recurring in the future. The #1 place for Learning Leaders to learn from each other. Get the data & knowledge you need to succeed in the era of AI. We're an invite-only community for L&D leaders to learn from each other through expert-led roundtables, our active forum, and data-driven resources. To analyze the root cause, ask questions such as: What factors contributed to the problem? Were there any design flaws or inconsistencies in the assembly instructions? Did the team encounter any challenges during the assembly process? Were there any issues with the quality of the materials or components used? By examining these factors, you can gain insights into the root cause of the assembly issue and develop strategies to address it effectively. Implementing Solutions Once you have identified the problem and analyzed the root cause, it’s time to implement solutions. This step involves taking corrective actions to resolve the assembly issue and ensure a successful outcome. Implementing solutions may include: Adjusting the assembly process or sequence to address the root cause. Providing additional training or guidance to the assembly team. Modifying the assembly instructions to clarify or rectify any ambiguities. Collaborating with stakeholders to improve the quality of materials or components. It’s important to document the solutions implemented to create a record of the troubleshooting process. This documentation will be valuable in refining future assembly instructions and optimizing assembly processes. For more information on effective assembly instructions, you may find our article on efficient assembly methods helpful. By following a systematic approach to troubleshooting assembly issues, you can overcome challenges and ensure a smooth assembly process. Remember to continuously learn from past issues, seek feedback from the assembly team, and incorporate lessons learned into future assembly instructions. With effective troubleshooting practices in place, you can navigate assembly issues with confidence and achieve successful outcomes. Best Practices for Troubleshooting Assembly Issues When it comes to troubleshooting assembly issues, following best practices can help you identify and resolve problems efficiently. By adopting these practices, you can minimize downtime, increase productivity, and ensure a smoother assembly process. Here are three key best practices to consider: Preparing in Advance Preparation is key to effective troubleshooting. Before starting the assembly process, take the time to gather all the necessary information and resources. This includes reviewing the assembly instructions thoroughly and familiarizing yourself with the product or system you are assembling. By having a clear understanding of the assembly steps and requirements, you can anticipate potential issues and be better prepared to troubleshoot them. In addition to familiarizing yourself with the assembly instructions, ensure that you have all the tools, equipment, and materials required for the assembly. Having everything readily available will save you valuable time and prevent unnecessary delays during troubleshooting. You may also find it helpful to refer to our article on effective assembly instructions for further insights. Following a Systematic Approach When faced with assembly issues, it’s important to approach troubleshooting in a systematic manner. Start by identifying the problem or symptom that is causing the assembly process to stall or fail. This could be a misalignment, a missing part, or a malfunctioning component, among other possibilities. Once you have identified the problem, it’s crucial to analyze the root cause. Analyzing the root cause involves investigating the underlying reasons for the problem. This could include examining the assembly instructions, inspecting the parts, or consulting relevant team members. By understanding the root cause, you can implement appropriate solutions that address the problem at its source. For more guidance on troubleshooting, you may find our article on step-by-step assembly guide useful. Utilizing Available Resources When troubleshooting assembly issues, don’t hesitate to utilize the resources available to you. This can include reaching out to colleagues or experts who have experience with similar assembly processes. Collaborating with team members can provide fresh perspectives, additional insights, and potential solutions to the problem at hand. Furthermore, document and share the solutions that you implement during troubleshooting. This can be done through internal communication channels, such as knowledge-sharing platforms or project management tools. By documenting and sharing solutions, you contribute to the collective knowledge of your organization, enabling others to benefit from the troubleshooting process in the future. For more information on optimizing assembly processes, visit our article on optimizing assembly processes . By adhering to these best practices, you can troubleshoot assembly issues effectively, ensuring a smooth and efficient assembly process. Remember to prepare in advance, follow a systematic approach, and utilize available resources to overcome any challenges that may arise. With these practices in place, you’ll be well-equipped to handle troubleshooting and achieve successful assembly outcomes. Effective Communication for Troubleshooting When it comes to troubleshooting assembly issues, effective communication plays a vital role in resolving problems efficiently. Clear and open lines of communication help ensure that everyone involved is on the same page and working towards a common solution. In this section, we will explore three key aspects of effective communication for troubleshooting assembly issues: collaboration with team members, communicating with stakeholders, and documenting and sharing solutions. Collaboration with Team Members Collaboration with your team members is crucial when troubleshooting assembly issues. By fostering a collaborative environment, you encourage knowledge sharing, diverse perspectives, and creative problem-solving. Here are a few practices to facilitate effective collaboration: Foster open and respectful communication channels, encouraging team members to share their insights and ideas. Establish regular team meetings or check-ins to discuss ongoing issues and progress. Assign specific roles and responsibilities to team members to ensure efficient problem-solving. Encourage cross-functional collaboration, allowing individuals from different departments or teams to contribute their expertise. By collaborating effectively with your team members, you can tap into a wealth of knowledge and experience, increasing the likelihood of finding innovative solutions to assembly issues. Communicating with Stakeholders In addition to collaborating with your team members, effective communication with stakeholders is essential for troubleshooting assembly issues. Stakeholders may include managers, clients, suppliers, or other relevant parties involved in the assembly process. Here are some key practices for communicating with stakeholders: Clearly communicate the nature of the assembly issue, providing relevant details and context. Keep stakeholders informed about the progress of troubleshooting efforts, including any challenges or roadblocks encountered. Set realistic expectations regarding the timeline for issue resolution and communicate any potential impact on project schedules. Seek input and feedback from stakeholders, as they may provide valuable insights or alternative perspectives. Maintaining open and transparent communication with stakeholders helps build trust and ensures everyone is aligned in finding a resolution to the assembly issues. Documenting and Sharing Solutions Documenting and sharing solutions is crucial for effective troubleshooting in assembly processes. By capturing the steps taken to resolve issues, you create a valuable knowledge base that can be utilized for future reference. Here are some best practices for documenting and sharing solutions: Create a centralized repository or database to store troubleshooting information, making it easily accessible to the team. Document the identified problem, the analysis of the root cause, and the implemented solutions in a clear and concise manner. Include any relevant visuals, such as diagrams or images, to enhance understanding. Share the documented solutions with the team and stakeholders, ensuring that the information is readily available to all. By documenting and sharing solutions, you enable continuous improvement and empower others to handle similar assembly issues more efficiently in the future. Effective communication is the cornerstone of successful troubleshooting in assembly processes. By collaborating with team members, communicating with stakeholders, and documenting and sharing solutions, you create an environment that fosters innovation, problem-solving, and continual improvement. When everyone is on the same page and working together, assembly issues can be efficiently resolved, leading to smoother operations and improved productivity. Continuous Improvement in Assembly Instructions In the world of assembly instructions, continuous improvement is key to enhancing the assembly process and ensuring optimal outcomes. By learning from past issues, gathering feedback, and incorporating lessons learned, you can refine and optimize your assembly instructions for better performance. Learning from Past Issues One of the most valuable sources of improvement in assembly instructions is learning from past issues. When problems arise during the assembly process, it’s crucial to analyze and understand what went wrong. By examining the root causes of these issues, you can identify patterns and areas for improvement. To facilitate this learning process, it’s important to document and track assembly issues as they occur. This documentation can include details such as the specific problem, the steps leading up to it, and any solutions implemented. By maintaining a record of past issues, you can identify recurring problems and develop strategies to address them effectively. Feedback and Iteration Gathering feedback from those involved in the assembly process is another valuable tool for continuous improvement. Seek input from assembly line workers, supervisors, and other team members who have firsthand experience with the instructions. Their insights can provide valuable perspectives on areas that need improvement or clarification. Encourage open and honest communication regarding any challenges encountered during the assembly process. This feedback can help identify areas of confusion, ambiguities, or steps that may be prone to error. Actively listen to the feedback and use it as a basis for making necessary revisions to the assembly instructions. Iteration is key when it comes to improving assembly instructions. Based on the feedback received, revise the instructions to address the identified issues and make them clearer and more user-friendly. Repeat this process of collecting feedback, making revisions, and testing the updated instructions to ensure continuous improvement. Incorporating Lessons Learned Incorporating lessons learned from past issues and feedback is crucial for refining assembly instructions. As you identify areas for improvement, make the necessary updates to the instructions to address the root causes of the problems encountered. Consider incorporating visual aids such as diagrams, images, or videos to enhance clarity and understanding. These visual elements can help eliminate ambiguity and ensure that the assembly steps are clearly communicated. Additionally, revisit the assembly instructions periodically to ensure they remain up-to-date and aligned with any changes in the assembly process. Regularly reviewing and revising the instructions based on new insights and best practices helps to keep them relevant and effective. By actively learning from past issues, gathering feedback, and incorporating lessons learned, you can continuously improve your assembly instructions. The process of refinement and optimization will lead to more efficient assembly processes and better outcomes for everyone involved. For more insights on effective assembly instructions, check out our article on effective assembly instructions . Find the best expert for your next Project! Related blog posts. What to Know About Augmented Reality for eLearning Augmented reality (AR) is transforming the landscape of eLearning, offering unique and interactive ways to engage with educational content. ... Find the Best Time Management Facilitator in Miami: Tips for Hiring a Contractor for Your Training Needs Looking to boost productivity and manage your time effectively? Read this article on finding the perfect time management facilitator in Miam... Leveraging Nudge Theory in Corporate eLearning for Enhanced Outcomes Discover how to boost the effectiveness of corporate eLearning with the strategic application of Nudge Theory.... Join the #1 place for Learning Leaders to learn from each other. Get the data & knowledge you need to succeed in the era of AI. Join as a client or expert. We’ll help you get started Hire an Expert I’m a client, hiring for a project Find a job i’m a training expert, looking for work, get your free content. Enter your info below and join us in making learning the ultimate priority 🚀 Join as an employer or L&D expert I'm an employer, hiring for a project I'm an L&D expert, looking for work Already have an account? Login Want to learn and master x86-64 Assembly? Join Exercism’s x86-64 Assembly Track for access to 37 exercises with automatic analysis of your code and personal mentoring , all 100% free. About x86-64 Assembly 37 coding exercises for x86-64 assembly on exercism. from collatz conjecture to atbash cipher.. Get better at programming through fun, rewarding coding exercises that test your understanding of concepts with Exercism. Collatz Conjecture Calculate the number of steps to reach 1 using the Collatz conjecture. Difference of Squares Find the difference between the square of the sum and the sum of the squares of the first N natural numbers. Atbash Cipher Create an implementation of the atbash cipher, an ancient encryption system created in the Middle East. Key Features of x86-64 Assembly Widely used. x86-64 has been the dominant instruction set for personal computer CPUs since 2010. As an assembly language, x86-64 cannot be beaten in pure execution speed. Cross-platform x86-64 has been adopted by AMD, Intel and VIA for their CPUs. With an enormous install base relying on stability, changes since introduction have been minimal. x86-64 powers the most capable desktop CPUs in the world. Detailed documentation Given its wide-spread and critical application, x86-64 has been exactingly documented. Get mentored the x86-64 Assembly way Every language has its own way of doing things. x86-64 Assembly is no different. Our mentors will help you learn to think like a x86-64 Assembly developer and how to write idiomatic code in x86-64 Assembly. Once you've solved an exercise, submit it to our volunteer team, and they'll give you hints, ideas, and feedback on how to make it feel more like what you'd normally see in x86-64 Assembly - they'll help you discover the things you don't know that you don't know. Community-sourced x86-64 Assembly exercises The x86-64 Assembly track on Exercism has 37 exercises to help you write better code. Discover new exercises as you progress and get engrossed in learning new concepts and improving the way you currently write. Get started with the x86-64 Assembly track The best part, it’s 100% free for everyone. Assembly Tutorial Assembly - Home Assembly - Introduction Assembly - Environment Setup Assembly - Basic Syntax Assembly - Memory Segments Assembly - Registers Assembly - System Calls Assembly - Addressing Modes Assembly - Variables Assembly - Constants Assembly - Arithmetic Instructions Assembly - Logical Instructions Assembly - Conditions Assembly - Loops Assembly - Numbers Assembly - Strings Assembly - Arrays Assembly - Procedures Assembly - Recursion Assembly - Macros Assembly - File Management Assembly - Memory Management Assembly Useful Resources Assembly - Quick Guide Assembly - Useful Resources Assembly - Discussion Selected Reading UPSC IAS Exams Notes Developer's Best Practices Questions and Answers Effective Resume Writing HR Interview Questions Computer Glossary Assembly Programming Tutorial Assembly language is a low-level programming language for a computer or other programmable device specific to a particular computer architecture in contrast to most high-level programming languages, which are generally portable across multiple systems. Assembly language is converted into executable machine code by a utility program referred to as an assembler like NASM, MASM, etc. This tutorial has been designed for those who want to learn the basics of assembly programming from scratch. This tutorial will give you enough understanding on assembly programming from where you can take yourself to higher levels of expertise. Prerequisites Before proceeding with this tutorial, you should have a basic understanding of Computer Programming terminologies. A basic understanding of any of the programming languages will help you in understanding the Assembly programming concepts and move fast on the learning track. Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand OverflowAI GenAI features for Teams OverflowAPI Train & fine-tune LLMs Labs The future of collective knowledge sharing About the company Visit the blog Collectives™ on Stack Overflow Find centralized, trusted content and collaborate around the technologies you use most. Q&A for work Connect and share knowledge within a single location that is structured and easy to search. Get early access and see previews of new features. Program solving expression in assembly I have a problem with my simple program in assembly. I'm using DOSBox and TASM. The problem is that the operand types don't match in lines 76, 78, and 80. This is after multiplication. I tried to make some changes by using a different variable size. Post your code here directly. –  Carcigenicate Commented Jun 4, 2015 at 13:52 1 .. and mark the lines. In the paste lines 76 and 80 are empty, for example. I somehow doubt the error is there... –  Jester Commented Jun 4, 2015 at 13:54 What are the biggest numbers your program is suppose to handle? –  Jose Manuel Abarca Rodríguez Commented Jun 4, 2015 at 13:58 You've declared a and c as bytes. So add ax,a and mov ax,c would probably not do what you want even if they assembled. Make your variables words, or use extending mov s. –  Michael Commented Jun 4, 2015 at 14:01 2 Answers 2 Your program is almost good, you only have some issues with operand sizes, which is normal. So I took your code and made some little changes, those changes are commented and pointed by arrows (<========) and they are : Fixed the operand size problem. I still use DB because I noticed you are capturing the numbers as single chars. The result of (d-2*c) is stored in BX. This is because we need to divide (a+c*b) / (d-2*c), and you were popping (a+c*b) in BX, so, when you do div bx you were doing (d-2*c) / (a+c*b) . Separated the display for quotient and remainder. Added 13,10 line breaks to messages. Fixed shl ax,2 by shl ax,1 . One shl is x2, two shl are x2x2. The remainder is obtained from dl because when div uses a word as divisor, the remainder is left in dx . Here is your code with the little changes (tested on EMU8086): Next is your "to do" list: Change the size of operands from DB to DW, to allow your program to handle bigger numbers. Change DIV by IDIV, because DIV is unsigned while IDIV is signed. IDIV will let you handle negative results. Capture numbers with int=21h ah=0Ah as strings (not as single chars). Later, you convert the strings into numbers. Next two links will take you to the procedures to convert from string to number : Assembly x86 Date to Number - Breaking a string into smaller sections 32 bit Calculator in 8086 Assembly Finally, the test data : Thank You . Now i will make it more usefull like You said :> –  Mack Commented Jun 4, 2015 at 15:55 This correctly (I think) evaluates (a+c*b) / (d-2*c) , not following the order of operations / operator precedence in the (a+c*b)/d -2*c formula the question asked for. It's weird to give the remainder from an intermediate part of an expression, but that's how formulas work. (Unless it was incorrectly transcribed from math notation like how $\frac{ (a+c*b }{ d-2*c } prints. –  Peter Cordes Commented Dec 27, 2020 at 15:54 Because this question is an big success at 9k views and because the accepted answer is essentially wrong and misguiding , I decided to post a correct version so people can finally find out how to calculate these simple expressions. I have problem with program. Operand types do not match at line 76 78 80. add ax,a ; line 76 push ax mov ax,c ; line 78 shl ax,2 sub d,ax ; line 80 In most assembly instructions the size of the operands on both sides of the comma must match. Since you have defined your a , b , c , and d variables as bytes , you cannot legally use them with the word -sized register AX . That's why TASM gave your the error message. When evaluating an expression like (a+c*b)/d-2*c , you have to respect the algebraic rules. items that are parenthesised get calculated as a whole for items that are not parenthesised you need to follow the normal precedence rules: * and / come before + and - Redundantly parenthesizing everything we get: (a+c*b)/d-2*c <=> ((a+(c*b))/d)-(2*c) when sets of parenthesis are nested the inner set has precedence over the outer set Considering that a , b , and c are single digit numbers from 0 to 9, and that d is a single digit number from 1 to 9, the result can range from -18 to 72. Therefore we can calculate the whole expression using byte-sized operations. It's not necessary to use the signed division idiv since the dividend at that point will always be positive. Please notice that we used just one register ( AX ) to find the result. Would you have expected this? Below is my implementation of it all. I only left out the part that displays the quotient and remainder, but I have provided a link to Displaying numbers with DOS that explains in great detail how you can output signed and unsigned numbers. It's the basic stuff that you simply must know, so it's never gonna be a waste of time if you read it whole. @PeterCordes I did retag the question from equation to expression , but missed the same thing in my answer. Thanks for the edit. –  Sep Roland Commented Dec 27, 2020 at 15:55 Cheers, glad you agree that people should use math terminology correctly, and that I'm not the only person bothered by people "solving" simple formulae / expressions and calling them equations. :) –  Peter Cordes Commented Dec 27, 2020 at 16:19 Your Answer Reminder: Answers generated by artificial intelligence tools are not allowed on Stack Overflow. Learn more Sign up or log in Post as a guest. Required, but never shown By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy . Not the answer you're looking for? Browse other questions tagged assembly expression x86-16 tasm dosbox or ask your own question . The Overflow Blog Where does Postgres fit in a world of GenAI and vector databases? Mobile Observability: monitoring performance through cracked screens, old... 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DSA Tutorial Data Structures Linked List Dynamic Programming Binary Tree Binary Search Tree Divide & Conquer Mathematical Backtracking Branch and Bound Pattern Searching Assembly Line Scheduling | DP-34 Assembly line scheduling is a manufacturing problem. In automobile industries assembly lines are used to transfer parts from one station to another station. – Manufacturing of large items like car, trucks etc. generally undergoes through multiple stations, where each station is responsible for assembling particular part only. Entire product be ready after it goes through predefined n stations in sequence.  – Manufacturing of car may be done through several stages like engine fitting, coloring, light fitting, fixing of controlling system, gates, seats and many other things. -The particular task is carried out at the station dedicated to that task only. Based on the requirement there may be more than one assembly line. -In case of two assembly lines if the load at station j at assembly 1 is very high, then components are transfer to station of assembly line 2 the converse is also true. This technique helps to speed ups the manufacturing process.  -The time to transfer partial product from one station to next station on the same assembly line is negligible. During rush factory may transfer partially completed auto from one assembly line to another, complete the manufacturing as quickly as possible. Assembly line scheduling is a problem in operations management that involves determining the optimal sequence of tasks or operations on an assembly line to minimize production costs or maximize efficiency. This problem can be solved using various data structures and algorithms. One common approach is dynamic programming, which involves breaking the problem down into smaller sub-problems and solving them recursively. The following is an overview of the steps involved in solving an assembly line scheduling problem using dynamic programming: Define the problem: The first step is to define the problem, including the number of tasks or operations involved, the time required to perform each task on each assembly line, and the cost or efficiency associated with each task. Define the sub-problems: Next, we need to define the sub-problems by breaking down the problem into smaller pieces. In assembly line scheduling, this involves determining the optimal sequence of tasks for each station along the assembly line. Define the recurrence relation: The recurrence relation defines the relationship between the sub-problems and the overall problem. In assembly line scheduling, the recurrence relation involves computing the minimum cost or maximum efficiency of the assembly line by considering the cost or efficiency of the previous station and the time required to transition to the next station. Solve the sub-problems: To solve the sub-problems, we can use a table or matrix to store the minimum cost or maximum efficiency of each station. We can then use this table to determine the optimal sequence of tasks for the entire assembly line. Trace the optimal path: Finally, we can trace the optimal path through the table or matrix to determine the sequence of tasks that minimizes production costs or maximizes efficiency. A car factory has two assembly lines, each with n stations. A station is denoted by S i,j where i is either 1 or 2 and indicates the assembly line the station is on, and j indicates the number of the station. The time taken per station is denoted by a i,j . Each station is dedicated to some sort of work like engine fitting, body fitting, painting, and so on. So, a car chassis must pass through each of the n stations in order before exiting the factory. The parallel stations of the two assembly lines perform the same task. After it passes through station S i,j , it will continue to station S i,j+1 unless it decides to transfer to the other line. Continuing on the same line incurs no extra cost, but transferring from line i at station j – 1 to station j on the other line takes time t i,j . Each assembly line takes an entry time e i and exit time x i which may be different for the two lines. Give an algorithm for computing the minimum time it will take to build a car chassis. The below figure presents the problem in a clear picture:    The following information can be extracted from the problem statement to make it simpler:  Two assembly lines, 1 and 2, each with stations from 1 to n. A car chassis must pass through all stations from 1 to n in order(in any of the two assembly lines). i.e. it cannot jump from station i to station j if they are not at one move distance. The car chassis can move one station forward in the same line, or one station diagonally in the other line. It incurs an extra cost ti, j to move to station j from line i. No cost is incurred for movement in same line. The time taken in station j on line i is a i, j . S i, j represents a station j on line i. Breaking the problem into smaller sub-problems:   We can easily find the ith factorial if (i-1)th factorial is known. Can we apply the similar funda here?  If the minimum time taken by the chassis to leave station S i, j-1 is known, the minimum time taken to leave station S i, j can be calculated quickly by combining a i, j and t i, j . T1(j) indicates the minimum time taken by the car chassis to leave station j on assembly line 1. T2(j) indicates the minimum time taken by the car chassis to leave station j on assembly line 2. Base cases:   The entry time e i comes into picture only when the car chassis enters the car factory. Time taken to leave the first station in line 1 is given by:  T1(1) = Entry time in Line 1 + Time spent in station S 1,1   T1(1) = e 1 + a 1,1   Similarly, time taken to leave the first station in line 2 is given by:  T2(1) = e 2 + a 2,1 Recursive Relations:   If we look at the problem statement, it quickly boils down to the below observations:  The car chassis at station S 1,j can come either from station S 1, j-1 or station S 2, j-1 . Case #1: Its previous station is S 1, j-1   The minimum time to leave station S 1,j is given by:  T1(j) = Minimum time taken to leave station S 1, j-1 + Time spent in station S 1, j   T1(j) = T1(j-1) + a 1, j Case #2: Its previous station is S 2, j-1   The minimum time to leave station S1, j is given by:  T1(j) = Minimum time taken to leave station S 2, j-1 + Extra cost incurred to change the assembly line + Time spent in station S 1, j   T1(j) = T2(j-1) + t 2, j + a 1, j The minimum time T1(j) is given by the minimum of the two obtained in cases #1 and #2.  T1(j) = min((T1(j-1) + a 1, j ), (T2(j-1) + t 2, j + a 1, j ))  Similarly, the minimum time to reach station S2, j is given by:  T2(j) = min((T2(j-1) + a 2, j ), (T1(j-1) + t 1, j + a 2, j )) The total minimum time taken by the car chassis to come out of the factory is given by:  Tmin = min(Time taken to leave station S i,n + Time taken to exit the car factory)  Tmin = min(T1(n) + x 1 , T2(n) + x 2 ) Assembly line Scheduling Using  R ecursion : Time Complexity: O(2^n) where n = number of stations Auxiliary Space: O(n) as the recursion depth of the function is proportional to n, so the space required by the function call stack is also O(n) Why dynamic programming?   The above recursion exhibits overlapping sub-problems. There are two ways to reach station S 1, j :  From station S 1, j-1 From station S 2, j-1 So, to find the minimum time to leave station S 1, j the minimum time to leave the previous two stations must be calculated(as explained in above recursion). Similarly, there are two ways to reach station S 2, j :  Please note that the minimum times to leave stations S 1, j-1 and S 2, j-1 have already been calculated. So, we need two tables to store the partial results calculated for each station in an assembly line. The table will be filled in a bottom-up fashion. Note:   In this post, the word “leave” has been used in place of “reach” to avoid confusion. Since the car chassis must spend a fixed time in each station, the word leave suits better. Implementation:   Time Complexity: O(NUM_STATION), where NUM_STATION = number of stations Auxiliary Space: O(1) The bold line shows the path covered by the car chassis for given input values. We need only the last two values in the auxiliary arrays. So instead of creating two arrays, we can use two variables. Time Complexity: O(n), where n = number of stations Auxiliary Space: O(1) Exercise:   Extend the above algorithm to print the path covered by the car chassis in the factory. References:   Introduction to Algorithms 3rd Edition by Clifford Stein, Thomas H. Cormen, Charles E. Leiserson, Ronald L. Rivest This article is compiled by Aashish Barnwal .   Please Login to comment... Similar reads. SUMIF in Google Sheets with formula examples How to Get a Free SSL Certificate Best SSL Certificates Provider in India Elon Musk's xAI releases Grok-2 AI assistant Content Improvement League 2024: From Good To A Great Article Improve your Coding Skills with Practice What kind of Experience do you want to share? 9 Scenarios of Common Assembly Line Issues by Dan McKiernan , on Sep 8, 2015 5:15:00 AM To explain how eFlex Assembly might support the assembly line issues you are facing, the following are 9 common scenarios we frequently hear from engineers. 1. Over (or Under) Producing Due to a Change in Demand Are dramatic changes in your industry forcing you to rethink your manufacturing strategies? There is a new landscape emerging that requires manufacturers to move and change at lightning speed. Whether you’re experiencing changes in the market for lower (or higher) demand for specific products, an inflexible assembly line and lack of proper tools makes rebalancing your assembly line costly and time consuming. The Solution Rapidly accommodate production schedule changes due to spikes in customer demand with eFlex Assembly. You can easily rebalance your assembly line within hours to meet changing demands with eFlex Assembly’s Process Configuration Tool and its “plug-n-play” hardware and software architecture. 2. Diminishing Returns on Lean Manufacturing Efforts If your company has successfully embraced lean methods for assembly, but is now seeing diminishing returns from your Kaizen efforts, it may be time for a paradigm shift to keep PDCA moving. Stop “splitting hairs” in continuous improvement efforts and take the next step in lean assembly with technology. The technological advancements of eFlex Assembly can take you to the next level and provide a complete solution for your assembly operations. The modular design makes rebalancing or reconfiguring the line simply a matter of unplugging and re-plugging the equipment. Perform line changes with the Process Configuration Tool, instead of ladder logic. Validate a change with the Process Improvement Tool. Run line balance scenarios offline with the Process Engineering Tool. The software is all pre-written and validated, which eliminates development and debugging when rebalancing the line. 3. Lack of Real-Time Information Many manufacturing assembly lines do not have the infrastructure or the tools to identify problem areas and analyze the entire assembly line process from one central location. Without accurate, ongoing, real-time information about your assembly line, you are not equipped to foresee potential issues or quickly react to them when they arise. Whether you need ongoing information, periodic status updates or data to observe a recent line change, it is imperative to have a tool to continually monitor and analyze your assembly line. The Process Improvement Tool in eFlex Assembly provides you with real-time, continuous and standardized task level data to provide analysis for every station in your assembly process. With a good understanding of your assembly line, you can easily identify problems and make accurate decisions to meet the changing demands of your assembly line. 4. Unbalanced Station Workloads If some of your assembly line stations are underutilized or over utilized, you are likely experiencing bottlenecks and efficiency issues. One reason your line may be poorly balanced is because it was based on industry timing standards and documents which did not accurately reflect the real task timing at each station. The quality control, data collection and statistical analysis available with eFlex Assembly works well with all station types. The line balance simulator in the Process Engineering Tool takes advantage of the built-in time study of all interlocked tasks. This timing information allows you to continuously average those tasks and have more actual time estimates to appropriately balance the work. The ability to rebalance lines is best realized in the stations with direct manual labor, although it can help automated assembly lines that are inherently more rigid and specialized. 5. WIP or Manufacturing Cycle Time If there is a lack of knowledge about your assembly line process and/or unrealistic production quotas, you may be experiencing unnecessary buffers and product storage areas (WIP) that are negatively impacting your bottom line. The Process Improvement Tool in eFlex Assembly evaluates cycle times (takt times), non-conforming product related to tasks, manufacturing lead time and WIP. Therefore, you will have real-time data to easily identify where unnecessary WIP is occurring for you to assess how best to reduce or eliminate the issues causing this waste. 6. Lengthy Changeover Time Do you need a solution for quicker manufacturing line changeovers? You may be reducing or eliminating changeovers because of the cost and time needed to conduct a lengthy changeover process, and as a result are overproducing inventory. eFlex Assembly is a production line life cycle management tool with an inherent adaptability that can do diverse tasks, at varying rates, with on-the-fly changeover, in far less time than previously possible. The “plug-n-play” architecture with agreed upon standardize processes can cut your changeover time in half. Depending on the complexity of the changeover, eFlex Assembly will also provide the error proofing and efficiency to make the changeover smoother. 7. Late Product Launches on New Assembly Lines When launching a new assembly line, you may find it difficult to develop both the product and the assembly line within the typical aggressive program timing requirements. Traditionally, the product is developed and then each station process is clarified prior to building the assembly line, which takes considerable time when done in this order. When launching a new assembly line, the advantage of eFlex Assembly is that you can simultaneously develop the product and the assembly line process to meet aggressive delivery deadlines. Both end user and the assembly line builder benefit from proceeding with the manufacturing of the new assembly line in parallel. 8. Low Production Quality Without the proper tools, you may have difficulty identifying the station(s) or location(s) causing quality issues within the assembly process. When implementing changes to improve quality, you also may not know how the changes are impacting line efficiency. With eFlex Assembly, easily pinpoint quality issues at the source of the problem because the stations are interlocked to ensure high quality before they release a part to the next station. Once you implement a change to improve quality, the standardized analytics in the Process Improvement Tool will help you evaluate the current status of your line’s quality and cycle time to determine how a recent change has impacted your line quality and efficiency. 9. Late Product Launches on Existing Assembly Lines When modifying an existing assembly line for a new product or model within a given timeframe, the launch may be delayed due to time consuming and expensive reconfiguration, including redefining and hard coding each station in the line. Simultaneously develop the product and the assembly line process to meet aggressive customer delivery deadlines with eFlex Assembly. When modifying an existing assembly line, the Process Configuration Tool provides a central configuration location to quickly reconfigure your entire assembly line in hours without recoding or stopping operations. Our team is a creative bunch that loves learning and pushing the limits to find the best solutions for today's lean manufacturers.  Internal discussions at the office might range from new features that manufacturing process control software should have to machine learning, blockchain technology, or what the future of AR on the plant floor looks like. 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Tienken Rd. Rochester Hills, MI 48306 Contact Sales [email protected] Quick Links Request a Demo Client Portal Open a Ticket Terms of Service Privacy Policy Cookie Settings Epicor Connected Process Control Copyright 2024 Epicor Solving Problems How do we solve our problems? by Alexandra Palmer Suitable for Whole School (Pri) To use the book  We’re Going on a Bear Hunt  and the Bible story of David and Goliath to explore how to deal with life’s problems. Preparation and materials Have available the book We’re Going on a Bear Hunt by Michael Rosen and Helen Oxenbury. Alternatively, have available the YouTube video ‘Michael Rosen performs We’re Going on a Bear Hunt’ and the means to show it during the assembly. It is 5.02 minutes long and is available at: https://www.youtube.com/watch?v=0gyI6ykDwds You will also need to be familiar with the Bible story of David and Goliath. (A summary of the story is provided in the ‘Assembly’, Step 4.) Ask the children what they like about the story. Possible answers could include the actions, the repetition, the sound of the words (onomatopoeia) or simply that it’s fun. The story of We’re Going on a Bear Hunt  teaches us many things, like how it feels to get outside, enjoy the great outdoors and have adventures with our families and friends. But the most important thing we learn is how to deal with problems when they happen. In the story, whenever the group come across a problem that stops them from trying to find the bear, they say, ‘We can’t go over it. We can’t go under it. Oh, no! We’ve got to go through it!’ By saying this, they aren’t avoiding the problem; instead, they are sorting it out by dealing with it and pressing on. In the Bible, there is a story called David and Goliath that deals with a problem. Ask the children what they know about David and Goliath and the problem that the people in the story were facing. The answer is that the Israelites were fighting their enemies, who were called the Philistines. The problem was Goliath, who was one of the Philistines. Goliath was a giant and the Israelites were too scared to fight him. One of the Israelites, David, was a shepherd boy who was asked by his dad to deliver some food to his brothers, who were part of the Israelite army. While David was with his brothers, he saw Goliath and discovered that nobody was prepared to fight him. David volunteered to fight Goliath because he was used to fighting off lions with his slingshot while looking after his father’s sheep. King Saul, the leader of the Israelite army, heard what David intended to do, and offered him his armour. David tried it on, but it was too big and the sword was too heavy for him to use. So, David decided to wear his normal clothes and use his slingshot for a weapon. As David walked out to meet Goliath, he picked up five stones to use in his slingshot. When Goliath saw David, he laughed, but David used his slingshot and a stone to knock Goliath down and win the battle. The story of David and Goliath is a good model for how we can sort out problems in our own lives. When David saw Goliath, he could have thought, ‘Uh-oh, he’s too big!’ and then run away from him. Running away and avoiding a problem is not the right thing to do, even though it may seem like the best or easiest thing to do at the time. In the story, David trusts God and sees that Goliath is big, but God is even bigger! Maybe David thought: Can’t go over him. Can’t go under him. Goliath’s not thin. Goliath’s not slim. Oh, yes, I’ll use my sling and one stone. God’s on my side, so I’m not alone! The Israelites were avoiding the problem of Goliath because they were scared and didn’t want to deal with him. They were running away from the problem, whereas David decided to solve it. Even though it can be scary dealing with problems, it is always the right thing to do. Time for reflection While we are at school, we are going to encounter many problems, such as falling out with friends, sorting out whose game to play at break-time, getting our homework completed, losing our jumper or learning tricky spellings for a spelling test. Let’s not run away from these problems. Remember, ‘We can’t go over it. We can’t go under it. Oh, no! We’ve got to go through it!’ Let’s always talk to our friends, family or teachers because they will help us with problems. Let’s also remember to be ourselves when sorting out problems, rather than pretending to be somebody we’re not. In the story of David and Goliath, King Saul wanted David to wear his armour, but David knew that he wouldn’t be able to wear it and fight Goliath because it was too heavy. So, when problems do happen, it’s important that we sort them out in the way that suits us best. Point out that even today in school, children might be facing a problem. Remind them that it is always best to share a problem. Encourage them to talk to a teacher if there is something they need help with. Prayer Dear God, Thank you for authors who write amazing books. We pray that when any of us have problems, we will seek help. Thank you that we have friends, family and teachers who are always there when we need help. Amen. The YouTube video ‘Our God is a great big God’. It is 3 minutes long and is available at: https://www.youtube.com/watch?v=eaXPXWBcE3I Quality in Assembly: Problem-Solving System Helps Cabinet Maker Win Share This Story Restricted Content You must have JavaScript enabled to enjoy a limited number of articles over the next 30 days. Related Articles Quality in assembly: machine vision helps carmakers ensure quality, quality in assembly: software helps assemblers manage quality tasks, solving the problem of tin whiskers, related products. Strong Supply Chains Through Resilient Operations: Five Principles for Leaders to Win in a Volatile World Kaizen assembly: designing, constructing, and managing a lean assembly line. Digital Manufacturing and Assembly Systems in Industry 4.0 Related directories, tri-mation industries, quality bearings & components, never miss the latest news and trends driving the manufacturing industry, stay in the know on the latest assembly trends.. Copyright ©2024. All Rights Reserved BNP Media. Design, CMS, Hosting & Web Development :: ePublishing Assembly: Problem Solving This assembly supports learners to understand key concepts related to the early steps of Problem Solving. It starts by defining the skill and considering key themes, before identifying the skill in action. The themes are explored through three simple exercises, followed by a chance to reflect on their own skills. Also in this assembly Resource properties Join the growing community of teachers and facilitators already helping learners master eight essential skills for education, enterprise and employment. This site is protected by reCAPTCHA and the Google privacy policy and terms of service apply. New here? Sign up Forgot your login? Please wait... Forgot your password? Click here By clicking “Enter”, you agree to our terms and conditions and privacy policy. This site is protected by reCAPTCHA and the Google privacy policy and terms of service apply. By clicking “Continue”, you agree to our terms and conditions and privacy policy. This site is protected by reCAPTCHA and the Google privacy policy and terms of service apply. To provide a comprehensive learning experience and optimal site use, we will occasionally send you emails about the Hub. If you would prefer not to receive these, please email [email protected] . Create a group to measure your group's skills progress over time and get suggested resources pitched at the right level. There are eight essential skills. Each skill is broken down into 16 teachable, measurable steps from beginner to mastery. You can filter resources by age or stage. Measure your group's progress on the Dashboard and find suggested resources. For more support with how to use Skills Builder Hub and teach the eight essential skills, go to Help & Training. Manage your invitation to Invite staff to join. Copy the link to share with staff so that they can join 's Hub account: Your colleagues click on the link to login to their existing Hub account or setup a new Hub account. Their account will automatically be linked to 's Hub account. They will then appear in the list of staff account. Please note: The invitation link will expire after days. Add to favourites Add this resource to the favourites for your group to use later. Track progress for Tell us why Please tell us a little more about what you think about Assembly: Problem Solving. Search anything: Assembly Line Scheduling using Dynamic Programming Algorithms dynamic programming (dp). Open-Source Internship opportunity by OpenGenus for programmers. Apply now. In an product industry, produts are produced using assembly lines. Multiple lines are worked together to produce a useable product and completed useable product exits at the end of the line. For making a product in the optimal time we should choose the optimised assembly line from a station so that a company can make product in the best utilized time. Problem Statement The main goal of solving the Assembly Line Scheduling problem is to determine which stations to choose from line 1 and which to choose from line 2 in order to minimize assembly time. In the above the diagram we have two main assembly line consider as LINE 1 and LINE 2. Parameters are: S[i,j] : The jth station on ith assembly line a[i,j] : Time required at station S[i,j], because every station has some dedicated job that needs to done. e[i] : Entry time of product on assembly line i [here i= 1,2] x[i] : Exit time from assembly line i t[i,j] : Time required to transit from station S[i,j] to the other assembly line. Hence, the input consist of: Normally, when a raw product enters an assembly line it passes through through that line only. Therefore, the time to go from one station to another station of same assembly line is negligible but to pass a partially completed product from one station of a line to other station of another line a t[i,j] is taken. It is a optimization problem in which we have to optimized the total assembly time. To solve the optimization problem we make use of Dynamic Programming. To solve with DP we will see how it have Overlapping Subproblem and Optimal Substructure. Consider that f[i,j] denotes the fastest time taken to get the partially completed product from starting point through ith line and jth station. The DP structure is as follows: Consider the above image, we can reach S[1,j] in two ways, either from station S[1,j-1] or from station S[2,j-1] . We have to find the minimum time from both the ways:- Time taken to reach from 1st line will be, f[1,j-1] + a[1,j] . Time taken to reach from 2nd line will be, f[2,j-1] + t[2,j-1] + a[1,j] . If the partial product comes from S[2,j-1], additionally it incurs the transfer cost to change the assembly line (like t[2,j-1]). Note that , minimum time to leave S1[j-1] and S2[j-1] have already been calculated. We can notice from this example that the approach is using the already solved time from f[1,j-1], so the Overlapping Subproblem is used. And to find the fastest way through station j, we solve the sub-problems of finding the fastest way through station j-1 which is the Optimal Substructure . Breaking in smaller sub-problems We will use the Bottom-Up approach to find the minimum time to complete a product and for that consider f1 & f2 be time taken from line 1 & 2 respectively and 'e' & 'x' are the entry & exiting time respectively. The following are the cases that we will use: Base-Case: At station 1 at partial product directly comes from entry point, therefore f1[1]= e1 + a[1,1] and f2[1]= e2 + a[2,1] . For calculating time to reach at jth station from line 1 we will find the optimal time as we discussed above, f[1,j]= min{f1[j-1]+a[i,j], f2[j-1]+t[2,j-1]+a[1,j]} The optimized or fastest time to exit a completed product will be f optimal = min{f1[n] + x1, f2[n] + x2} . We need two tables to store the partial results calculated for each station in an assembly line. The table will be filled in a bottom-up fashion. Pseudo Code for Assembly Line Scheduling where 'a' denotes the assembly costs, 't' denotes the transfer costs, 'e' denotes the entry costs, 'x' denotes the exit costs and 'n' denotes the number of assembly stages. Implementation in C++ Following is our C++ implementation of solving the Assembly Line Scheduling problem using Dynamic Programming: Output: Optimal Time for completing the product is: 37 Workflow of solution As a[2][5] defined in code denotes that we have 2 assembly line and 5 stations. Then f1[0] and f2[0] is defined by adding entry time (e[i]) and first station time. Then applies the recursive solution for n station points, the l1[j] denotes from which assembly line partial product comes from. We will choose the optimized time by calculating minimum time by continuing on the same assembly time or by changing the assembly line (if line changed then t[i][j-1] time will also be added). At last f optimal is calculated by minimum of the time at the last station, added with the exiting time of the line from which the product exit. Time Complexity As the dp tabulation array is used and the 'n' iteration is done to store the optimal time in the array, therefore the time complexity of the above Dynamic Programming implementation of the assembly line scheduling is O(n) . We are storing the optimal time taken to pass through station in an array, therefore the space complexity will be O(n). 224 IMAGES Day 1 : Assembly Problem Solving & Conflict Resolution Problem Solving Solving Problems Assembly PowerPoint for children KS1 & KS2 for Top 10 Problem Solving Templates with Samples and Examples Day 5 Assembly Problem Solving & Conflict Resolution Component Assembly to support the scientific problem solving process in VIDEO Clutch assembly problem Whirlpool washing machine #trending #whirlpoolwashingmachine #shorts Gaocheng 21v machine Gear assemble تعلم Assembly #10 blocks Petrol station . Building blocks for kids "Introduction to Programming: The Basics of Algorithms and Languages .NET Framework : Assemblies COMMENTS Assembly: What is Problem Solving? This assembly supports learners to understand key concepts related to the early steps of Problem Solving. It starts by defining the skill and considering key themes, before identifying the skill in action. The themes are explored through three simple exercises, followed by a chance to reflect on their own skills. Exercises: Assembly 6186 assembly syntax is based on x86-64 assembly, and like the x86-64, 6186 registers are 64 bits wide. However, the 6186 has a different set of registers. There are just five general-purpose registers, %ra , %rb, %rr, %rx, and %ry. (" [W]hen she tries to be deadly serious she is speaking under…constraint".) SPCK Assemblies To encourage a positive approach to problem solving. by The Revd Alan M. Barker. Suitable for Whole School (Pri) Aims. To encourage a positive approach to problem-solving. Preparation and materials. ... Assembly. Place the half-full glass on a table. Invite everyone to listen to the fable of Aesop, and to join in the story with 'thumbs up' when ... PDF CMU School of Computer Science CMU School of Computer Science 40 Basic Practices in Assembly Language Programming 4. If you can use registers, don't use memory. A basic rule in assembly language programming is that if you can use a register, don't use a variable. The register operation is much faster than that of memory. The general purpose registers available in 32-bit are EAX, EBX, ECX, EDX, ESI, and EDI. Themes for Morning Assembly in Schools Unleashing Creativity and Innovation Theme for Daily School Assembly Concepts. Fostering a Growth Environment for Creativity and Innovation: Celebrating creativity in all its forms. Encouraging Out-of-the-Box Thinking and Problem-solving: Engaging students in creative problem-solving exercises. Solving Problems (primary) Some people may have no idea of what they want to do in the long term We look at how for these peope tackling the short term procrastination can be useful. Solving Problems. £3.50. Add To Cart. From this pack -. Primary Pack 1 - Download. £40.00. From Hurdles to Success: Navigating Troubleshooting Assembly Issues The first step in troubleshooting assembly issues is to identify the specific problem or challenge you are facing. This requires careful observation and analysis of the assembly process. Common assembly issues may include misalignment, faulty components, incomplete connections, or difficulties with specific steps. x86-64 Assembly on Exercism About x86-64 Assembly. x86-64 assembly is the programming language for the 64-bit version of the x86 instruction set. It is based on the original 8086 instruction set from 1978. Assembly language is different from high-level languages like C# and Java. There are no variables, objects, or loops. Assembly language program to find largest number in an array Problem - Determine largest number in an array of n elements. Value of n is stored at address 2050 and array starts from address 2051. Result is stored at address 3050. Starting address of program is taken as 2000. Example: Program: Explanation: Registers used: A, H, L, C. INX H increases value of HL by 1. Amazon.com: ShenMaster Electronic Puzzle Games STEM Toy for Boys Buy ShenMaster Electronic Puzzle Games STEM Toy for Boys & Girls Kids Age 5-7-8-10 with 600 Challenges, Flame Brain Teaser ，Education Board Game-Develop Primitive Reasoning & Problem Solving Skills: Assembly & Disentanglement Puzzles - Amazon.com FREE DELIVERY possible on eligible purchases Assembly Programming Tutorial Assembly Programming Tutorial. Assembly language is a low-level programming language for a computer or other programmable device specific to a particular computer architecture in contrast to most high-level programming languages, which are generally portable across multiple systems. Assembly language is converted into executable machine code by ... PDF Assembly Practice Problems Assembly Practice Problems. Assembly Practice Problems. 1. 1. In this problem, you will write a. complete assembly program. (i.e., an assembly program along with any relevant assembler directives) to manipulate two data tables, one being an input table located within program memory and one being an output table located within data memory. PDF A3 Problem Solving: A Case of Assembly Line Downtime teamwork. A3 is a structured and very useful problem-solving template that brings all these components together. There are many materials in relation to establishing A3 lean problem solving in different industries globally. Anderson (2011) in sector of education, described the results of a short survey among 22 students who used A3reporting in a - Program solving expression in assembly I have problem with program. Operand types do not match at line 76 78 80. add ax,a ; line 76 push ax mov ax,c ; line 78 shl ax,2 sub d,ax ; line 80 In most assembly instructions the size of the operands on both sides of the comma must match. Search Skills Builder Hub This assembly supports learners to understand key concepts related to the early steps of Problem Solving. It starts by defining the skill and considering key themes, before identifying the skill in action. The themes are explored through three simple exercises, followed by a chance to reflect on their own skills. 8D and A3 Formalize Problem-Solving The A3 approach is named after the paper size that is used for the root-cause analysis and corrective action. A3 does the same thing as 8D; it provides guidance for solving a problem and a method for communicating the actions taken and results to the team. The A3 approach encourages engineers to create graphical representations of the problem ... Assembly Line Scheduling This problem can be solved using various data structures and algorithms. One common approach is dynamic programming, which involves breaking the problem down into smaller sub-problems and solving them recursively. The following is an overview of the steps involved in solving an assembly line scheduling problem using dynamic programming: 9 Scenarios of Common Assembly Line Issues Many manufacturing assembly lines do not have the infrastructure or the tools to identify problem areas and analyze the entire assembly line process from one central location. Without accurate, ongoing, real-time information about your assembly line, you are not equipped to foresee potential issues or quickly react to them when they arise. ... Video: 6 Key Behaviors that Define Excellence in Problem-Solving This podcast episode delves into the facets of Jamie Flinchbaugh's latest book, People Solve Problems. Explore how to improve problem-solving skills within your organization with Flinchbaugh, the founder of JFlinch and an author with over 30 years of experience helping leaders build and improve teams across various industries.A note from the author, "Problem-solving effectiveness is critical ... SPCK Assemblies Ask the children what they know about David and Goliath and the problem that the people in the story were facing. The answer is that the Israelites were fighting their enemies, who were called the Philistines. The problem was Goliath, who was one of the Philistines. Goliath was a giant and the Israelites were too scared to fight him. Quality in Assembly: Problem-Solving System Helps Cabinet Maker Win Quality in Assembly: Problem-Solving System Helps Cabinet Maker Win. A strand of ribbon isn't much, but for one Michigan assembler, it may just have led to a 2008 Shingo Prize for Operational Excellence. At the Metalworks assembly plant in Ludington, MI, a worker installs drawer cushions. Photo courtesy Metalworks Great Openings. Assembly: What is Problem Solving? Assembly: Problem Solving. This assembly supports learners to understand key concepts related to the early steps of Problem Solving. It starts by defining the skill and considering key themes, before identifying the skill in action. The themes are explored through three simple exercises, followed by a chance to reflect on their own skills. Assembly Line Scheduling using Dynamic Programming Problem Statement. The main goal of solving the Assembly Line Scheduling problem is to determine which stations to choose from line 1 and which to choose from line 2 in order to minimize assembly time. In the above the diagram we have two main assembly line consider as LINE 1 and LINE 2. Parameters are: S[i,j]: The jth station on ith assembly line essay homework paper phd project resume review study thesis