Bitwise and logical operatorsDifference Between Bitwise and Logical Operators in PHP

The distinction between bitwise operators and logical operators operators is often overlooked and confused. They are often used one for another: it is true they have some overlapping domains of application, and yet, their functionality differ significantly. Here’s a breakdown of how these operators work:

Logical Operators: Booleans at Play

Logical operators in PHP operate on boolean values and return boolean results. For example:

<?php
  var_dump(true && true); // Evaluates to true
?>

These operators are often represented using integers, specifically 0 and 1, where 0 is equivalent to false and 1 is equivalent to true. Consider the following example:

<?php
  var_dump(1 || 0); // Evaluates to true
?>

Under the hood, PHP casts any value to a boolean before processing it with a logical operator. This ensures that logical operations are consistently boolean-focused.

Bitwise Operators: Working with Integers

Bitwise operators, on the other hand, operate directly on integers. They treat integers as binary representations and perform logical operations, bit by bit. Hence, the name of bitwise operators. For instance:

<?php
  var_dump(0 & 3); // Evaluates to 0, not false
  var_dump(5 & 3); // Evaluates to 1
?>

Here’s what happens, in binary notation, in the second example:

  101 (5 in binary)
& 011 (3 in binary)
  ---
  001 (1 in binary)

Each bit in the integer is evaluated using the corresponding logical operation, and the result is placed in the corresponding position of the resulting integer. Finally, this result is returned as an integer.

The Systemic Perspective

From a broader perspective, you can think of bitwise operators as logical operators applied to multiple values simultaneously. For example, an 8-bit integer could be viewed as eight boolean values, with bitwise operators processing all bits in parallel.

Overlap Between Bitwise and Logical Operators

While logical and bitwise operators serve different purposes, there is some functional overlap. Notably:

  • !$a: Negates the value of $a. For example, if $a is true or 0, !$a is false.
  • ~$a: Negates all the bits in $a. For instance, if $a is 0, ~$a is -1, and not 1, although both are loosely equal to true. if $a is 1, ~$a is -2, and not false.

Then, their behavior diverges when $a is not strictly 0 or 1, making it essential to understand their respective contexts.

Conclusion

Logical operators are works well for boolean logic, in particular for any true/false conditions. Bitwise operators, on the other hand, offer a powerful way to manipulate integers at the binary level, making them invaluable for tasks that involve low-level data processing.