Will this code set and clear zero and sign flags

[joblaise]

I'm a beginning and am having problems with this code. I think my problem is with my data statement. Please provide help. Here's the code:

.data
.386
.model flat, stdcall
option casemap :none ; case sensitive
.code
main PROC

mov cl,1 ; CL=1
sub cl,1 ; CL=0, SF=0, ZF=1
call DumpRegs

sub cl,1 ; CL=-1, SF=1, ZF=0
call DumpRegs

add ch,1 ; CH=0, SF=0, ZF=1
call DumpRegs

add ch,1 ; CH=1, SF=0, ZF=0
call DumpRegs

exit
main ENDP
END main

[NoHero]

To manipulate the CPU flags you can use the pushf and popf functions. The push and pop the flag register onto the stack. With that you can retrieve the flags modify them and set them back.

pushf
pop ax
; Now modify them, they are in ax
push ax
popf

/ 10 posts to go

[joblaise]

Thanks for the response. I see that you used an alternative method, which is good to know. However, I was wondering if the code I wrote could be used, and if so, what am I doing wrong to make it execute properly?

Thanks in advance for your help.

[OReubens]

Originally Posted by joblaise

Thanks for the response. I see that you used an alternative method, which is good to know. However, I was wondering if the code I wrote could be used, and if so, what am I doing wrong to make it execute properly?

Thanks in advance for your help.

Well, you never set CH to anything, so the call

add ch,1 ; CH=0, SF=0, ZF=1
call DumpRegs

Will not do as you think (not what's in the comment).

I'm guessing you wanted to use CL instead of CH.


You can also manipulate set flags via
- SAHF (sotre AH into flags). This will only modify the lower 8 bits of the flags. 'extended' 32bit flags won't be changed.

Direction, interupt enable, Carry flags can be set/cleared directly via CLD/STD, CLI/STI, CLC/STC