[loops] While, Do While, For loops in Assembly Language (emu8086)

I want to convert simple loops in high-level languages into assembly language (for emu8086) say, I have this code:

 for(int x = 0; x<=3; x++)
 {
  //Do something!
 }

or

 int x=1;
 do{
 //Do something!
 }
 while(x==1)

or

 while(x==1){
 //Do something
 }

How do I do this in emu8086?

This question is related to loops for-loop assembly while-loop x86-16

The answer is


For-loops:

For-loop in C:

for(int x = 0; x<=3; x++)
{
    //Do something!
}

The same loop in 8086 assembler:

        xor cx,cx   ; cx-register is the counter, set to 0
loop1   nop         ; Whatever you wanna do goes here, should not change cx
        inc cx      ; Increment
        cmp cx,3    ; Compare cx to the limit
        jle loop1   ; Loop while less or equal

That is the loop if you need to access your index (cx). If you just wanna to something 0-3=4 times but you do not need the index, this would be easier:

        mov cx,4    ; 4 iterations
loop1   nop         ; Whatever you wanna do goes here, should not change cx
        loop loop1  ; loop instruction decrements cx and jumps to label if not 0

If you just want to perform a very simple instruction a constant amount of times, you could also use an assembler-directive which will just hardcore that instruction

times 4 nop

Do-while-loops

Do-while-loop in C:

int x=1;
do{
    //Do something!
}
while(x==1)

The same loop in assembler:

        mov ax,1
loop1   nop         ; Whatever you wanna do goes here
        cmp ax,1    ; Check wether cx is 1
        je loop1    ; And loop if equal

While-loops

While-loop in C:

while(x==1){
    //Do something
}

The same loop in assembler:

        jmp loop1   ; Jump to condition first
cloop1  nop         ; Execute the content of the loop
loop1   cmp ax,1    ; Check the condition
        je cloop1   ; Jump to content of the loop if met

For the for-loops you should take the cx-register because it is pretty much standard. For the other loop conditions you can take a register of your liking. Of course replace the no-operation instruction with all the instructions you wanna perform in the loop.


Examples related to loops

How to increment a letter N times per iteration and store in an array? Angular 2 Cannot find control with unspecified name attribute on formArrays What is the difference between i = i + 1 and i += 1 in a 'for' loop? Prime numbers between 1 to 100 in C Programming Language Python Loop: List Index Out of Range JavaScript: Difference between .forEach() and .map() Why does using from __future__ import print_function breaks Python2-style print? Creating an array from a text file in Bash Iterate through dictionary values? C# Wait until condition is true

Examples related to for-loop

List append() in for loop Prime numbers between 1 to 100 in C Programming Language Get current index from foreach loop how to loop through each row of dataFrame in pyspark TypeScript for ... of with index / key? Is there a way in Pandas to use previous row value in dataframe.apply when previous value is also calculated in the apply? Python for and if on one line R for loop skip to next iteration ifelse How to append rows in a pandas dataframe in a for loop? What is the difference between ( for... in ) and ( for... of ) statements?

Examples related to assembly

Why does C++ code for testing the Collatz conjecture run faster than hand-written assembly? While, Do While, For loops in Assembly Language (emu8086) Replacing a 32-bit loop counter with 64-bit introduces crazy performance deviations with _mm_popcnt_u64 on Intel CPUs How to run a program without an operating system? Difference between "move" and "li" in MIPS assembly language Carry Flag, Auxiliary Flag and Overflow Flag in Assembly How do AX, AH, AL map onto EAX? JNZ & CMP Assembly Instructions Difference between JE/JNE and JZ/JNZ The point of test %eax %eax

Examples related to while-loop

While, Do While, For loops in Assembly Language (emu8086) MySQL Insert with While Loop Python loop to run for certain amount of seconds How to break a while loop from an if condition inside the while loop? How to find sum of several integers input by user using do/while, While statement or For statement Python: How to keep repeating a program until a specific input is obtained? Creating multiple objects with different names in a loop to store in an array list ORA-06502: PL/SQL: numeric or value error: character string buffer too small How to break out of a loop in Bash? for or while loop to do something n times

Examples related to x86-16

While, Do While, For loops in Assembly Language (emu8086) What's the purpose of the LEA instruction?