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

Question

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?

Answer 1

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.