Right Shift

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$result = $value >> $steps;

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Technical Mechanics

1. Type Casting: PHP automatically casts both $value and $steps to integers before performing the bitwise operation. Floating-point numbers are truncated.
2. Arithmetic Shift: PHP implements an arithmetic right shift, meaning it preserves the sign bit (the most significant bit). PHP does not have a logical (zero-fill) right shift operator.
3. Bit Discarding: Bits shifted past the least significant bit (position 0) are permanently discarded.
4. Sign Extension: Vacated bit positions on the left (the most significant side) are filled with the original sign bit. They are filled with 0 for positive integers and 1 for negative integers (which are represented in two’s complement).
5. Mathematical Equivalence: Shifting an integer right by $n positions is mathematically equivalent to integer division by $2^n$, rounded towards negative infinity: floor($value / (2 ** $steps)).

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Syntax Visualization

$a = 12;       // Binary: 00000000 ... 00001100
$b = $a >> 2;  // Binary: 00000000 ... 00000011 (Decimal: 3)

// The two rightmost bits (00) are discarded.
// Two 0s are shifted in from the left.

$x = -12;      // Binary: 11111111 ... 11110100 (Two's complement)
$y = $x >> 2;  // Binary: 11111111 ... 11111101 (Decimal: -3)

// The two rightmost bits (00) are discarded.
// Two 1s are shifted in from the left to preserve the negative sign.

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Edge Cases and Constraints

• Negative Shift Steps: Attempting to shift by a negative number of steps ($value >> -1) throws an ArithmeticError in PHP 7.0 and later.
• Overshifting: Shifting by an amount greater than or equal to the bit width of the system’s integer type (typically 64 bits) results in undefined behavior. PHP inherits this behavior directly from C and does not implement software checks to zero out the result. On most modern architectures (such as x86_64), the CPU masks the shift amount modulo the bit width. Consequently, shifting a 64-bit integer by 64 positions ($value >> 64) is evaluated by the hardware as $value >> (64 % 64), which equals $value >> 0. This typically returns the original $value rather than 0 or -1.
• String Operands: If strings are passed to the operator, PHP attempts to convert them to integers. If the string is non-numeric, a TypeError is thrown in PHP 8.0+.