Geração de GUID Automático em PHP

function v4() {
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)
);
}