CHAPTER 19. MANIPULATING SPECIFIC BIT(S) CHAPTER 19. MANIPULATING SPECIFIC BIT(S)
_rt$ = -8 ; size = 4
_i$ = -4 ; size = 4
_a$ = 8 ; size = 4
_f PROC
push ebp
mov ebp, esp
sub esp, 8
mov DWORD PTR _rt$[ebp], 0
mov DWORD PTR _i$[ebp], 0
jmp SHORT $LN4@f
$LN3@f:
mov eax, DWORD PTR _i$[ebp] ; increment of i
add eax, 1
mov DWORD PTR _i$[ebp], eax
$LN4@f:
cmp DWORD PTR _i$[ebp], 32 ; 00000020H
jge SHORT $LN2@f ; loop finished?
mov edx, 1
mov ecx, DWORD PTR _i$[ebp]
shl edx, cl ; EDX=EDX<<CL
and edx, DWORD PTR _a$[ebp]
je SHORT $LN1@f ; result of AND instruction was 0?
; then skip next instructions
mov eax, DWORD PTR _rt$[ebp] ; no, not zero
add eax, 1 ; increment rt
mov DWORD PTR _rt$[ebp], eax
$LN1@f:
jmp SHORT $LN3@f
$LN2@f:
mov eax, DWORD PTR _rt$[ebp]
mov esp, ebp
pop ebp
ret 0
_f ENDP