String reverse in another way - php

Question

I'm searching for a function which can reverse a string in another way.
it should always takes the last and the first char of the string.
In example the string
123456
should become
615243
Is there any php function?
EDIT
This is my code so far
$mystring = "1234";
$start = 0;
$end = strlen($mystring);
$direction = 1;
$new_str = '';
while ($start === $end) {
if ($direction == 0) {
$new_str .= substr($mystring, $start, 1);
$start++;
$direction = 1;
} else {
$new_str .= substr($mystring, $end, -1);
$end--;
$direction = 0;
}
}

Answer 1

I couldn't help myself, I just had to write your code for you...
This just takes your string, splits it into an array, then builds up your output string taking letters from the front and end.
$output = '';
$input = str_split('123456');
$length = count($input);
while(strlen($output) < $length) {
$currLength = strlen($output);
if($currLength % 2 === 1) {
$output .= array_shift($input);
}
else {
$output .= array_pop($input);
}
}
echo $output;
Example: http://ideone.com/Xyd0z6

Answer 2

Not very different from Scopey's answer with a for loop:
$str = '123456';
$result = '';
$arr = str_split($str);
for ($i=0; $arr; $i++) {
$result .= $i % 2 ? array_shift($arr) : array_pop($arr);
}
echo $result;

Answer 3

This should work for you:
<?php
$str = "123456";
$rev = "";
$first = substr($str, 0, strlen($str)/2);
$last = strrev(substr($str, strlen($str)/2));
$max = strlen($first) > strlen($last) ? strlen($first): strlen($last);
for($count = 0; $count < $max; $count++)
$rev .= (isset($last[$count])?$last[$count]:"" ) . (isset($first[$count])?$first[$count]: "");
echo $rev;
?>
Output:
615243