Comparing two numbers in M86k assembly

I'm trying to write a min-sort subroutine, but the CMP instruction has me confused. Does it do overflow checking for you, or do I need to check for overflows and then flip the result on overflow? The documentation that I have to work with is not very good to say the least.

Have I got this right:

signed (pseudocode)

Code:

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CMP src, dest
if Z=1, jump to _end_
if V=0, jump to _sort_
EXG src,dest
_sort_:
if N=1, jump to _end_ ; dest>src
EXG src,dest
_end_:
; the register situation will be: src<=dest

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I'm not quite sure how to handle the unsigned representation ...

It works exactly like subtract, except the "destination" register is not modified.

It's been a long time since I wrote 68K assembler, but I think this is right:

Code:

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    cmp  D1, D0
    bge  _end
    exg  D1, D0

_end:
    ret

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I you may need to swap the BGE for a BLE instruciton.

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Mats

Doh, I should've looked at the branch jumps first. You use BGE for signed and BCC for unsigned. So yeah, your program will work for signed numbers.

Quote:

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Originally Posted by Memloop

Doh, I should've looked at the branch jumps first. You use BGE for signed and BCC for unsigned. So yeah, your program will work for signed numbers.

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Yes, and I beleive from your original post that you wanted a signed conversion - otherwise, why are you trying to look at the N bit of the condition code?

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Mats

What do you mean? The branch jump for BGE is N exor V = 0, so surely you must check the N flag?