Помощь php

function RealFileSize($fp)
{
    $pos = 0;
    $size = 1073741824;
    fseek($fp, 0, SEEK_SET);
    while ($size > 1)
    {
        fseek($fp, $size, SEEK_CUR);

        if (fgetc($fp) === false)
        {
            fseek($fp, -$size, SEEK_CUR);
            $size = (int)($size / 2);
        }
        else
        {
            fseek($fp, -1, SEEK_CUR);
            $pos += $size;
        }
    }

    while (fgetc($fp) !== false)  $pos++;

    return $pos;
}

<?php
$a = fopen($filename, 'r');
fseek($a, 0, SEEK_END);
$filesize = ftell($a);
fclose($a);
?>