uuid generation in pure php

pure-php-uuid.php

<?php

/* generate rfc compliant v3,v4 and v5 uuids
 * http://www.php.net/manual/en/function.uniqid.php#94959
 * $type -> uuid version to generate (3, 4 or 5)
 * $namespace -> namespace for v3 and v5 uuids
 * $name -> string for v3 and v5 uuids
 */
function generate_uuid($type, $namespace = null, $name = null) {
    switch($type) {
        case 3:
        case 5:
            // Validate namespace and make sure name is not null
            if(!valid_uuid($namespace) || empty($name)) return false;
            // Get hexadecimal components of namespace
            $nhex = str_replace(array('-','{','}'), '', $namespace);
            // Binary Value
            $nstr = '';
            // Convert Namespace UUID to bits
            for($i = 0; $i < strlen($nhex); $i+=2) {
                $nstr .= chr(hexdec($nhex[$i].$nhex[$i+1]));
            }
            // Set hash value and version string for v3 and v5
            if ($type == 3) {
                $hash = md5($nstr . $name);
                $vnum = 0x3000;
            } else {
                $hash = sha1($nstr . $name);
                $vnum = 0x5000;
            }
            return sprintf('%08s-%04s-%04x-%04x-%12s',
                // 32 bits for "time_low"
                substr($hash, 0, 8),
                // 16 bits for "time_mid"
                substr($hash, 8, 4),
                // 16 bits for "time_hi_and_version",
                // four most significant bits holds version number
                (hexdec(substr($hash, 12, 4)) & 0x0fff) | $vnum,
                // 16 bits, 8 bits for "clk_seq_hi_res",
                // 8 bits for "clk_seq_low",
                // two most significant bits holds zero and one for variant DCE1.1
                (hexdec(substr($hash, 16, 4)) & 0x3fff) | 0x8000,
                // 48 bits for "node"
                substr($hash, 20, 12)
            );
        break;
        case 4:
            return sprintf('%04x%04x-%04x-%04x-%04x-%04x%04x%04x',
                // 32 bits for "time_low"
                mt_rand(0, 0xffff), mt_rand(0, 0xffff),
                // 16 bits for "time_mid"
                mt_rand(0, 0xffff),
                // 16 bits for "time_hi_and_version",
                // four most significant bits holds version number 4
                mt_rand(0, 0x0fff) | 0x4000,
                // 16 bits, 8 bits for "clk_seq_hi_res",
                // 8 bits for "clk_seq_low",
                // two most significant bits holds zero and one for variant DCE1.1
                mt_rand(0, 0x3fff) | 0x8000,
                // 48 bits for "node"
                mt_rand(0, 0xffff), mt_rand(0, 0xffff), mt_rand(0, 0xffff)
            );
        break;
        default:
            return false;
        break;
    }
}