Quick introduction to reverse engineering for beginners

4.1.3 Task 1.3
This is standard C function too, actually, two functions working in pair. Source code taken from MSVC
2010 and modified sligthly.
The matter of modification is that this function can work properly in multi-threaded environment, and
I removed its support for simplification (or for confusion).
Compiled in MSVC 2010 with /Ox flag.
_BSS SEGMENT
_v DD 01H DUP (?)
_BSS ENDS
_TEXT SEGMENT
_s$ = 8 ; size = 4
f1 PROC
push ebp
mov ebp, esp
mov eax, DWORD PTR _s$[ebp]
mov DWORD PTR _v, eax
pop ebp
ret 0
f1 ENDP
_TEXT ENDS
PUBLIC f2
_TEXT SEGMENT
f2 PROC
push ebp
mov ebp, esp
mov eax, DWORD PTR _v
imul eax, 214013 ; 000343fdH
add eax, 2531011 ; 00269ec3H
mov DWORD PTR _v, eax
mov eax, DWORD PTR _v
shr eax, 16 ; 00000010H
and eax, 32767 ; 00007fffH
pop ebp
ret 0
f2 ENDP
_TEXT ENDS
END
Same code compiled in GCC 4.4.1:
public f1
f1 proc near
arg_0 = dword ptr 8
push ebp
mov ebp, esp
mov eax, [ebp+arg_0]
mov ds:v, eax
pop ebp
retn
f1 endp
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