Is it a bad practice to use the flag case as a boolean return value?

Question

I am writing some procedures in x86 assembler that modify ZF as a means to return booleans, so I can do something like this:

call is_value_correct
jz not_correct

I am wondering if this is considered bad practice, as some coding standards suggest that simple values ​​should be returned in the AX register.

Answer 1

Yes, do this if your code is faster and / or smaller .

asm , . "" , .

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# inputs:   foo in EAX (zero-extended into RAX), bar in EDI
# pre-requisites: DF=0
# clobbers: RCX, RDX, AL (but not the rest of EAX)
# returns:  AL = something,  ZF = something else
my_func:
   ...
   setc al
   ...
   something that sets ZF
   ret

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