CMP in assembly language

loops assembly cmp
Jay Jenkins picture Jay Jenkins · Jul 19, 2012 · Viewed 10.6k times · Source

So I have this line of code:

LOOP CMP Y, #0
BEQ DONE - When it is equal go to DONE.
ADD X, #1 - add decimal constant 1 to x.
SUB Y, #1 - subtract decimal constant 1 from y
B LOOP - branch loop (start the loop again)
DONE ...

I just read that CMP means subtracting the operand from Rn (Y minus 0) And that CMN means adding the operand to the Rn (0 + Y for example)

The first line (LOOP CMP Y, #0): I thought this just compares Y with the number 0. Is this true?

Answer

Jerry Coffin picture Jerry Coffin · Jul 19, 2012

Yes -- cmp (at least in most assembly languages) does a subtraction. It sets the flags based on the result of that subtraction, but then throws away the result itself.

Related questions

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 } …

Read More
Writing a while loop in assembly

I'm trying to write a while loop in assembly with a 6502 processor and I cannot figure out how to write the hexadecimal code. I've seen examples written using the shorthand where there is a label for where the loop should …

Read More
For-each over an array in JavaScript

How can I loop through all the entries in an array using JavaScript? I thought it was something like this: forEach(instance in theArray) Where theArray is my array, but this seems to be incorrect.

Read More