SeededRandomNumberGenerator.php

<?php

class SeededRandomNumberGenerator
{
    /**
     * An integer with the 32 least significant bits set
     * 0xffffffff is a float on 32-bit platforms :-/
     */
    private const MASK = \PHP_INT_SIZE === 4 ? ~0 : 0xffffffff;

    /**
     * @var int
     */
    private $seed;

    /**
     * @param int $seed
     */
    public function __construct(int $seed)
    {
        $this->seed = $seed & self::MASK;
    }

    /**
     * Add two integers, wrap around on overflow (avoid float coersion)
     * https://stackoverflow.com/questions/4068033/add-two-integers-using-only-bitwise-operators
     *
     * @param int $a
     * @param int $b
     * @return int
     */
    private static function intAdd(int $a, int $b): int
    {
        $a &= self::MASK;
        $b &= self::MASK;

        $carry = $a & $b;
        $result = $a ^ $b;

        while ($carry) {
            $shiftedCarry = $carry << 1;
            $carry = $result & $shiftedCarry;
            $result ^= $shiftedCarry;
        }

        return $result & self::MASK;
    }

    /**
     * Multiply two integers, wrap around on overflow (avoid float coersion)
     * https://stackoverflow.com/questions/4456442/multiplication-of-two-integers-using-bitwise-operators
     *
     * @param int $a
     * @param int $b
     * @return int
     */
    private static function intMul(int $a, int $b): int
    {
        $a &= self::MASK;
        $b &= self::MASK;
        $result = 0;

        while ($b) {
            if ($b & 1) {
                $result = self::intAdd($result, $a);
            }

            $a = ($a << 1) & self::MASK;
            $b >>= 1;
        }

        return $result;
    }

    /**
     * Generate a pseudo-random number between 0 and 65535 from the current seed
     * https://stackoverflow.com/questions/4768180/rand-implementation
     *
     * @return int
     */
    public function generate(): int
    {
        return (($this->seed = self::intAdd(self::intMul($this->seed, 214013), 2531011)) >> 16) & 0xffff;
    }
}