generate UUID4 with pure PHP

UUID4.php

<?php

namespace Madapaja;

class UUID4
{
    protected $isUpperCase;

    public function __construct($isUpperCase = false)
    {
        $this->isUpperCase = !!$isUpperCase;
    }

    public function get($sep = '-')
    {
        $result = '';

        // time_low                     unsigned 32 bit integer
        $result .= $this->random(32);

        // "-"
        $result .= $sep;

        // time_mid                     unsigned 16 bit integer
        $result .= $this->random(16);

        // "-"
        $result .= $sep;

        // time_hi_and_version          unsigned 16 bit integer
        // version (0100)
        $result .= $this->hexString(1 << 2, 4);
        // time-hi
        $result .= $this->random(12);

        // "-"
        $result .= $sep;

        // clock_seq_hi_and_reserved    unsigned 8  bit integer
        // 10xxxxxx (x is random)
        $result .= $this->hexString(1 << 7 | mt_rand(0, pow(2, 6) - 1), 8);

        // clock_seq_low                unsigned 8  bit integer
        $result .= $this->random(8);

        // "-"
        $result .= $sep;

        // node                         unsigned 48 bit integer
        $result .= $this->random(48);

        return $result;
    }

    protected function random($bitNum)
    {
        $result = '';

        $bits = 16;
        $sum = 0;

        while ($bitNum != $sum && $bits > 0) {
            $bits = (($bitNum - $sum) > 16) ? 16 : $bitNum - $sum;
            $sum += $bits;

            $val = mt_rand(0, pow(2, $bits) -1);
            $result = $this->hexString($val, $bits) . $result;
        }

        return $result;
    }

    protected function hexString($val, $bits)
    {
        $digits = (int) ($bits / 4 + 0.9);
        return sprintf('%0' . $digits . ($this->isUpperCase ? 'X' : 'x'), $val);
    }
}

function uuid4($isUpperCase = false, $separator = '-')
{
    $obj = new UUID4($isUpperCase);
    return $obj->get($separator);
}

// generate UUID4
echo \Madapaja\uuid4();