Quick introduction to reverse engineering for beginners

public f2
f2 proc near
push ebp
mov ebp, esp
mov eax, ds:v
imul eax, 343FDh
add eax, 269EC3h
mov ds:v, eax
mov eax, ds:v
shr eax, 10h
and eax, 7FFFh
pop ebp
retn
f2 endp
bss segment dword public ’BSS’ use32
assume cs:_bss
dd ?
bss ends
4.1.4 Task 1.4
This is standard C library function. Source code taken from MSVC 2010. Compiled in MSVC 2010 with
/Ox flag.
PUBLIC _f
_TEXT SEGMENT
_arg1$ = 8 ; size = 4
_arg2$ = 12 ; size = 4
_f PROC
push esi
mov esi, DWORD PTR _arg1$[esp]
push edi
mov edi, DWORD PTR _arg2$[esp+4]
cmp BYTE PTR [edi], 0
mov eax, esi
je SHORT $LN7@f
mov dl, BYTE PTR [esi]
push ebx
test dl, dl
je SHORT $LN4@f
sub esi, edi
npad 6
$LL5@f:
mov ecx, edi
test dl, dl
je SHORT $LN2@f
$LL3@f:
mov dl, BYTE PTR [ecx]
test dl, dl
je SHORT $LN14@f
movsx ebx, BYTE PTR [esi+ecx]
movsx edx, dl
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