Bitwise Operations (AND/OR/XOR/NOT)

Bitwise operations work on individual bits, ignoring signed/unsigned concepts.

Core Operations

AND - both bits must be 1:

asm

mov al, 0b11001100
and al, 0b11110000    ; Result: 0b11000000

OR - at least one bit must be 1:

asm

mov al, 0b11001100
or  al, 0b00110011    ; Result: 0b11111111

XOR - bits must be different:

asm

mov al, 0b11001100
xor al, 0b11110000    ; Result: 0b00111100

NOT - flip all bits:

asm

mov al, 0b11001100
not al                ; Result: 0b00110011

Useful Examples

asm

# Zeroing a register (preferred method):
xor eax, eax    ; 2 bytes:  31 C0
mov eax, 0      ; 5 bytes:  B8 00 00 00 00

# Changing permissions
mov eax, 0b11100101 ; 101 r-x
or eax, 0b00000010  ; 111 rwx
and eax, 0b11111011 ; 011 -wx
xor eax, 0b00000010 ; 001 r--
and eax, 0b00000000 ; 000 ---