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103 lines (78 loc) · 3.94 KB
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"""
Bitwise operators manipulate integers at the individual bit level, serving as
essential tools in systems engineering, low-level protocols, and optimization.
While high-level Python code often abstracts away binary representations, bit-level
manipulation remains fundamental in production software engineering for:
- Permission & Flag Sets: Storing multiple boolean states (e.g., Read/Write/Execute,
feature flags) compactly within a single integer.
- Binary Protocol & Hardware Interfacing: Packing and unpacking binary payloads,
network headers, and device control registers.
- High-Performance Operations: Leveraging bit shifts (`<<`, `>>`) for fast power-of-two
scaling and constant-time bitwise operations.
- State Masking & Toggling: Testing specific bit fields with AND (`&`), setting flags
with OR (`|`), toggling states with XOR (`^`), and clearing bits with NOT (`~`).
"""
# Permission flags defined as distinct powers of two (individual bits)
PERM_READ = 1 << 0 # 0001 (1)
PERM_WRITE = 1 << 1 # 0010 (2)
PERM_EXECUTE = 1 << 2 # 0100 (4)
def has_permission(user_perms: int, perm: int) -> bool:
"""Check if a specific permission flag is enabled using bitwise AND."""
return (user_perms & perm) != 0
def add_permission(user_perms: int, perm: int) -> int:
"""Add a permission flag using bitwise OR."""
return user_perms | perm
def remove_permission(user_perms: int, perm: int) -> int:
"""Clear a permission flag using bitwise AND with NOT."""
return user_perms & ~perm
def toggle_permission(user_perms: int, perm: int) -> int:
"""Toggle a permission flag using bitwise XOR."""
return user_perms ^ perm
def main() -> None:
# 1. Fundamental bitwise arithmetic
a = 5 # Binary: 0101
b = 3 # Binary: 0011
# Bitwise AND (&) returns 1 only where both bits are 1
result_and = a & b # Binary: 0001 (Decimal: 1)
assert result_and == 1
# Bitwise OR (|) returns 1 if at least one bit is 1
result_or = a | b # Binary: 0111 (Decimal: 7)
assert result_or == 7
# Bitwise XOR (^) returns 1 where bits differ (one is 1, one is 0)
result_xor = a ^ b # Binary: 0110 (Decimal: 6)
assert result_xor == 6
# Bitwise NOT (~) inverts all bits, producing two's complement: -(x + 1)
result_not_a = ~a # Binary: 11111010 (Decimal: -6)
assert result_not_a == -6
# Bitwise left shift (<<) multiplies by powers of two (a * 2^2)
result_left_shift = a << 2 # Binary: 010100 (Decimal: 20)
assert result_left_shift == 20
# Bitwise right shift (>>) performs integer division by powers of two (a // 2^1)
result_right_shift = a >> 1 # Binary: 0010 (Decimal: 2)
assert result_right_shift == 2
# Operator precedence: arithmetic operations bind tighter than shifts
# https://docs.python.org/3/reference/expressions.html
result_shift_precedence = a >> 1 + 1 # Evaluates as a >> (1 + 1)
assert result_shift_precedence == 1 # 5 >> 2 -> 1
# 2. Practical engineering: Permission bitmask management
user_perms = 0
assert has_permission(user_perms, PERM_READ) is False
# Grant read and write permissions
user_perms = add_permission(user_perms, PERM_READ)
user_perms = add_permission(user_perms, PERM_WRITE)
assert user_perms == 3 # Binary: 0011
assert has_permission(user_perms, PERM_READ) is True
assert has_permission(user_perms, PERM_WRITE) is True
assert has_permission(user_perms, PERM_EXECUTE) is False
# Toggle write permission off
user_perms = toggle_permission(user_perms, PERM_WRITE)
assert has_permission(user_perms, PERM_WRITE) is False
assert user_perms == PERM_READ
# Add execute and remove read permissions
user_perms = add_permission(user_perms, PERM_EXECUTE)
user_perms = remove_permission(user_perms, PERM_READ)
assert user_perms == PERM_EXECUTE
assert has_permission(user_perms, PERM_EXECUTE) is True
assert has_permission(user_perms, PERM_READ) is False
if __name__ == "__main__":
main()