this post was submitted on 01 Feb 2024
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Programming

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not di does not seem to perform bitwise negation (lemmy.world)
submitted 5 months ago* (last edited 5 months ago) by qaz@lemmy.world to c/programming@programming.dev
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I've been trying to debug a program I'm working on and have managed to narrow it down to a single not statement. I fail to understand how this could fail. My current suspicion is the fact that I'm using a 16 bit (aka short) register. Should I even be using this?
Before not di 1101111110000000
Expected after not di 0010000001111111
Actually after not di 10000001111111

Code

.certain:
not di ; ← this line is the problem
bsf ax, di

GDB output

(gdb) p/t (short) $di $4 = 1101111110000000
(gdb) nexti
(gdb) p/t (short) $di $5 = 10000001111111
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[–] mrkite@programming.dev 20 points 5 months ago (4 children)

Your result is correct, is just not displaying the leading zeros.

[–] qaz@lemmy.world 2 points 5 months ago (2 children)

Do you perhaps know how to show the leading zeros?

[–] mrkite@programming.dev 3 points 5 months ago (1 children)

I'm not great with gdb but I think using the x cmd shows them.

[–] qaz@lemmy.world 1 points 5 months ago

Yes, but that doesn't seem to work with registers

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