If al is 0 (or rather, the result of or al, al
is 0, which only happens when al is 0), then it sets the zero flag. The jump (jz), tests the zero flag and jumps if it is set.
Question
print_string:
lodsb ; grab a byte from SI
cmp al, 0
;or al, al ; logical or AL by itself
jz .done ; if the result is zero, get out
mov ah, 0x0E
int 0x10h
I'm wondering how or al, al
works. I know that it tests to see if all of the characters in the string have been printed out? But I don't understand the logic.
Solution
OTHER TIPS
or al, al
sets the zero flag if the result is 0 (i.e. when al = 0), just as cmp al, 0
does. The useful difference between the two operations is that or al, al
has a smaller encoding on x86 architectures.
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