<?php
function hash_part($fp,$start,$length) {
        $ctx = hash_init('md5');
 
	$ch = "";
	$remaining=$length;
	$chunkSize=65536;
	while ($remaining > 0) {
		$data = fread($fp, $chunkSize);
		
		$read = hash_update($ctx, $data);
		$ch .= md5sum($data);
		
		$remaining -= strlen($data);
        }
	
        return hash_final($ctx) . " : " . md5sum($ch);
}

?>