Calculate sha1 thumbprint of ssl certificate

<?php
function sha1_thumbprint_pem($pem_file_contents)
{
    $file = $pem_file_contents;
    $file = preg_replace('/\-+BEGIN CERTIFICATE\-+/','',$file);
    $file = preg_replace('/\-+END CERTIFICATE\-+/','',$file);
    $file = trim($file);
    $file = str_replace( array("\n\r","\n","\r"), '', $file);
    $bin = base64_decode($file);
    return sha1($bin);
}
?>