I have got this so far:
mov esi,0
mov edi,LENGTHOF source - 2
mov ecx,SIZEOF source
L1:;iterate a loop
mov al,source[esi]
mov target[edi],al
inc esi
dec edi
loop L1
The target string should not have those characters at the end. I think I need to find the byte that needs to be zero and set it. How do I do that?
CodePudding user response:
Before
This is the source string0
%%%%
##########################
^^^^
After
This is the source string0
%%%0
gnirts ecruos eht si sihT#
^^^^
Because of
mov ecx,SIZEOF source
, the loop has one iteration too many! See how that 4th '%' was overwritten by 0.LENGTHOF source
tallies the characters and the terminating zero.LENGTHOF source - 1
will point at the offset where you need to write the new terminating zero in the target.
This is another version of the loop, one that avoids using the slow loop
instruction:
mov ecx, LENGTHOF source - 1 ; destination offset
xor ebx, ebx ; source offset
mov al, 0 ; terminating zero
L1: mov target[ecx], al
dec ecx
mov al, source[ebx]
inc ebx
test al, al ; until we reach terminator
jnz L1