Quick introduction to reverse engineering for beginners

add ebx, edx
lea esi, [esi+0]
loc_8048558: ; CODE XREF: f(int,int *,int *,int *)+CC
mov edx, [edi]
add eax, 1
add edi, 4
add edx, [esi]
add esi, 4
mov [ebx], edx
add ebx, 4
cmp ecx, eax
jg short loc_8048558
add esp, 0Ch
xor eax, eax
pop ebx
pop esi
pop edi
pop ebp
retn
; ---------------------------------------------------------------------------
loc_8048578: ; CODE XREF: f(int,int *,int *,int *)+52
cmp eax, esi
jnb loc_80484C1
jmp loc_80484F8
_Z1fiPiS_S_ endp
Almost the same, however, not as meticulously as Intel C++ doing it.
1.19.2 SIMD strlen() implementation
It should be noted that SIMD-instructions may be inserted into C/C++ code via special macros 73 . As of
MSVC, some of them are located in intrin.h file.
It is possible to implement strlen() function 74 using SIMD-instructions, working 2-2.5 times faster than
usual implementation. This function will load 16 characters into XMM-register and check each against zero.
size_t strlen_sse2(const char *str)
{
register size_t len = 0;
const char *s=str;
bool str_is_aligned=(((unsigned int)str)&0xFFFFFFF0) == (unsigned int)str;
if (str_is_aligned==false)
return strlen (str);
__m128i xmm0 = _mm_setzero_si128();
__m128i xmm1;
int mask = 0;
for (;;)
{
xmm1 = _mm_load_si128((__m128i *)s);
73 MSDN: MMX, SSE, and SSE2 Intrinsics
74 strlen() — standard C library function for calculating string length
99