microtime_diff.php

<?php
/**
 * Calculate a precise time difference.
 * @param string $start result of microtime()
 * @param string $end result of microtime(); if NULL/FALSE/0/'' then it's now
 * @return flat difference in seconds, calculated with minimum precision loss
 */
function microtime_diff($start, $end = null) {
	if (!$end) $end = microtime();

	list($start_usec, $start_sec) = explode(" ", $start);
	list($end_usec, $end_sec)     = explode(" ", $end);
	$diff_sec                     = intval($end_sec) - intval($start_sec);
	$diff_usec                    = floatval($end_usec) - floatval($start_usec);

	return floatval($diff_sec) + $diff_usec;
}