gistfile1.sh

$ uname -a
Linux betty 2.6.32-46-generic #108-Ubuntu SMP Thu Apr 11 15:55:01 UTC 2013 i686 GNU/Linux
$ php --version
PHP 5.3.2-1ubuntu4.19 with Suhosin-Patch (cli) (built: Mar 11 2013 15:23:47) 
Copyright (c) 1997-2009 The PHP Group
Zend Engine v2.3.0, Copyright (c) 1998-2010 Zend Technologies
    with Xdebug v2.2.1, Copyright (c) 2002-2012, by Derick Rethans


$ for i in {1..3}; do time php substrstrlen.php; done

real	0m24.045s
user	0m11.765s
sys	0m12.093s

real	0m24.106s
user	0m12.033s
sys	0m11.685s

real	0m24.160s
user	0m11.569s
sys	0m12.045s


$ for i in {1..3}; do time php strpos.php; done

real	0m11.865s
user	0m5.792s
sys	0m5.992s

real	0m11.865s
user	0m5.816s
sys	0m5.964s

real	0m12.549s
user	0m5.948s
sys	0m5.924s


$ for i in {1..3}; do time php substrstrlen_outside.php; done

real	0m12.665s
user	0m6.408s
sys	0m6.152s

real	0m12.642s
user	0m6.308s
sys	0m6.080s

real	0m12.576s
user	0m6.348s
sys	0m6.096s


...


# This run was in a VirtualBox VM with a much different configuration than 
# above, so it's probably best not to directly compare these to eachother.

$ uname -a
Linux precise32 3.2.0-23-generic-pae #36-Ubuntu SMP Tue Apr 10 22:19:09 UTC 2012 i686 i686 i386 GNU/Linux
$ php --version
PHP 5.3.10-1ubuntu3.6 with Suhosin-Patch (cli) (built: Mar 11 2013 14:34:31) 
Copyright (c) 1997-2012 The PHP Group
Zend Engine v2.3.0, Copyright (c) 1998-2012 Zend Technologies


$ for i in {1..3}; do time php substrstrlen.php; done

real	0m0.738s
user	0m0.708s
sys	0m0.024s

real	0m0.677s
user	0m0.636s
sys	0m0.036s

real	0m0.694s
user	0m0.664s
sys	0m0.028s


$ for i in {1..3}; do time php strpos.php; done

real	0m0.310s
user	0m0.260s
sys	0m0.044s

real	0m0.332s
user	0m0.296s
sys	0m0.032s

real	0m0.298s
user	0m0.280s
sys	0m0.012s


$ for i in {1..3}; do time php substrstrlen_outside.php; done

real	0m0.428s
user	0m0.396s
sys	0m0.028s

real	0m0.404s
user	0m0.376s
sys	0m0.024s

real	0m0.489s
user	0m0.464s
sys	0m0.016s

strpos.php

<?php 

$class = 'Symfony\Bundle\FrameworkBundle\DependencyInjection\Configuration';
$prefix = 'Twig_';

for ($i = 0; $i < 1000000; ++$i) {
    if (0 === strpos($class, $prefix)) {}
}

substrstrlen.php

<?php

$class = 'Symfony\Bundle\FrameworkBundle\DependencyInjection\Configuration';
$prefix = 'Twig_';

for ($i = 0; $i < 1000000; ++$i) {
    if (substr($class, 0, strlen($prefix)) === $prefix) {}
}

substrstrlen_outside.php

<?php

$class = 'Symfony\Bundle\FrameworkBundle\DependencyInjection\Configuration';
$prefix = 'Twig_';

$length = strlen($prefix);
for ($i = 0; $i < 1000000; ++$i) {
    if (substr($class, 0, $length) === $prefix) {}
}