guid.php

<?php
// GUID v4
public function guid() {
  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)
  );
}