PHP Bitwise Operators

Bitwise operators look at the tiny on-and-off switches inside a number instead of its total value. It is like flipping individual light switches in a row rather than reading the whole number.

In this page:

Bitwise AND and OR
Bitwise XOR (^)
Bitwise NOT (~)
Shift Operators (<<, >>)
Bitwise Flags Usage

Syntax

php

$result = $a & $b;   // AND
$result = $a | $b;   // OR
$result = $a ^ $b;   // XOR
$result = ~$a;       // NOT (flip every bit)

Bitwise AND and OR

Bitwise operators work on a number's individual binary digits rather than its overall value.

& sets each output bit to 1 only where *both* input bits were 1; | sets each output bit to 1 where *either* input bit was 1 — the same logic as &&/||, just applied bit by bit instead of to whole booleans.

Example: Bitwise AND and OR

php

<?php
echo 6 & 3, "\n"; // AND
echo 6 | 3;       // OR
?>

Bitwise XOR (^)

^ (XOR) sets each bit to 1 exactly where the two inputs disagree — one is 1 and the other is 0. Where the bits match, whether both 0 or both 1, the result bit is 0.

This bit-by-bit 'exactly one' behavior is what makes XOR useful for toggling flags on and off.

Example: Bitwise XOR (^)

php

<?php
// Print `6 ^ 3` to the output
echo 6 ^ 3;
?>

Bitwise NOT (~)

~ flips every bit of a number in one operation, turning every 1 into a 0 and every 0 into a 1.

Because of how negative numbers are represented in binary (two's complement), this ends up mathematically equivalent to -(x + 1) — a detail that trips people up until they've traced through an example.

Example: Bitwise NOT (~)

php

<?php
// Print `~5` to the output
echo ~5;
?>

Shift Operators (<<, >>)

<< shifts a number's bits left, filling the vacated positions on the right with zeros — the same effect as multiplying by a power of two.

>> shifts bits right, which has the effect of dividing by a power of two and discarding any remainder, making both useful as very fast alternatives to multiplication or division by 2.

Example: Shift Operators (<<, >>)

php

<?php
echo 4 << 1, "\n"; // multiply by 2
echo 4 >> 1;       // divide by 2
?>

Bitwise Flags Usage

A common real use is packing several independent yes/no flags into one integer, each represented by a single bit — checking $permissions & READ_FLAG tells you if that one flag is set, without needing a separate variable for every flag.

Example: Bitwise Flags Usage

php

<?php
// Call `define('READ_FLAG', 1)`
define('READ_FLAG', 1);
// Call `define('WRITE_FLAG', 2)`
define('WRITE_FLAG', 2);
// Declare `$permissions`, set to `READ_FLAG | WRITE_FLAG`
$permissions = READ_FLAG | WRITE_FLAG;
// Print a detailed dump (with types) of `(bool)($permissions & READ_FLAG)`
var_dump((bool)($permissions & READ_FLAG));
?>

Chapter Quiz — Complete all 8 topics to unlock

0/8 topics done

Complete these topics first:

← Previous Lesson PHP Logical Operators Next Lesson → PHP Assignment Operators