Description:
------------
When strpos() is given an index position to start searching, it actually performs 
more poorly than when the parameter is left off (thus defaulting to "0"). One 
would expect that giving it a starting index would improve performance since it 
could skip checking so many characters.

I've been able to reproduce this issue consistently with the attached script.

Two loops, each run 1 million times. The first loop specifies a start index of 2, 
whereas the second one doesn't specify one. You would expect the first loop to run 
faster. Try reversing this (giving the second loop a start index) and you will see 
the execution time results flip, as well.

My framework makes heavy use of strpos() and I discovered this issue when I 
attempted to optimize strpos() by skipping the first few characters of the string 
to be checked. No go.

Test script:
---------------
<?php

$k = 'image:0:{name}.{ext}';

$start = microtime(TRUE);

for ($i = 0; $i < 1000000; $i++) {
	strpos($k, '{', 2);
}

echo "<p>Seconds: ".(microtime(TRUE) - $start).'</p>';

$start = microtime(TRUE);

for ($i = 0; $i < 1000000; $i++) {
	strpos($k, '{');
}

echo "<p>Seconds: ".(microtime(TRUE) - $start).'</p>';

Expected result:
----------------
Specifying a start index would result in better performance since it has less to 
check.

Actual result:
--------------
Specifying a start index actually has a negative impact on the performance of the 
script, possibly due to logic where it must check if the index is positive or 
negative.