Quick introduction to reverse engineering for beginners

}
};
xmm1 = _mm_cmpeq_epi8(xmm1, xmm0);
if ((mask = _mm_movemask_epi8(xmm1)) != 0)
{
unsigned long pos;
_BitScanForward(&pos, mask);
len += (size_t)pos;
break;
}
s += sizeof(__m128i);
len += sizeof(__m128i);
return len;
(the example is based on source code from there).
Let’s compile in MSVC 2010 with /Ox option:
_pos$75552 = -4 ; size = 4
_str$ = 8 ; size = 4
?strlen_sse2@@YAIPBD@Z PROC ; strlen_sse2
push ebp
mov ebp, esp
and esp, -16 ; fffffff0H
mov eax, DWORD PTR _str$[ebp]
sub esp, 12 ; 0000000cH
push esi
mov esi, eax
and esi, -16 ; fffffff0H
xor edx, edx
mov ecx, eax
cmp esi, eax
je SHORT $LN4@strlen_sse
lea edx, DWORD PTR [eax+1]
npad 3
$LL11@strlen_sse:
mov cl, BYTE PTR [eax]
inc eax
test cl, cl
jne SHORT $LL11@strlen_sse
sub eax, edx
pop esi
mov esp, ebp
pop ebp
ret 0
$LN4@strlen_sse:
movdqa xmm1, XMMWORD PTR [eax]
pxor xmm0, xmm0
pcmpeqb xmm1, xmm0
pmovmskb eax, xmm1
test eax, eax
jne SHORT $LN9@strlen_sse
$LL3@strlen_sse:
100