fastest way to get a hash based on the githash in php

bench.php

<?php
/*
~>php bench.php
md5_file 634.3932 ms
hash_file/md5 714.4802 ms
parse contents 911.6130 ms
parse contents substr 852.8361 ms
contents first chunk 590.0660 ms

all ran with 30000 itterations
*/


$t = microtime(true);
for($i = 0;$i<30000;$i++) {
        md5_file('api/.git/FETCH_HEAD');
}
echo sprintf('md5_file %0.4f ms',(microtime(true)-$t)*1000)."\n";

$t = microtime(true);
for($i = 0;$i<30000;$i++) {
         hash_file('md5','api/.git/FETCH_HEAD');
}
echo sprintf('hash_file/md5 %0.4f ms',(microtime(true)-$t)*1000)."\n";

$t = microtime(true);
for($i = 0;$i<30000;$i++) {
        current(explode("\t",file_get_contents('api/.git/FETCH_HEAD')));
}
echo sprintf('explode contents %0.4f ms',(microtime(true)-$t)*1000)."\n";

$t = microtime(true);
for($i = 0;$i<30000;$i++) {
        $str = file_get_contents('api/.git/FETCH_HEAD');
        substr($str,0,strpos($str,"\t"));
}
echo sprintf('parse contents substr %0.4f ms',(microtime(true)-$t)*1000)."\n";

$t = microtime(true);
for($i = 0;$i<30000;$i++) {
        file_get_contents('api/.git/FETCH_HEAD',false,null,-1,40);
}
echo sprintf('contents first chunk %0.4f ms',(microtime(true)-$t)*1000)."\n";

$t = microtime(true);
for($i = 0;$i<30000;$i++) {

$versionNumber = filemtime(__DIR__.'/../.git/');
}
echo sprintf('md5_file %0.4f ms',(microtime(true)-$t)*1000)."\n";

on my system 28.3351 ms