public static function stablesort(&$array, $cmp_function = 'strcmp')
{
// Arrays of size < 2 require no action.
if (count($array) < 2) {
return;
}
// Split the array in half
$halfway = count($array) / 2;
$array1 = array_slice($array, 0, $halfway);
$array2 = array_slice($array, $halfway);
// Recurse to sort the two halves
self::stablesort($array1, $cmp_function);
self::stablesort($array2, $cmp_function);
// If all of $array1 is <= all of $array2, just append them.
if (call_user_func($cmp_function, end($array1), $array2[0]) < 1) {
$array = array_merge($array1, $array2);
return;
}
// Merge the two sorted arrays into a single sorted array
$array = [];
$ptr1 = $ptr2 = 0;
while ($ptr1 < count($array1) && $ptr2 < count($array2)) {
if (call_user_func($cmp_function, $array1[$ptr1], $array2[$ptr2]) < 1) {
$array[] = $array1[$ptr1++];
} else {
$array[] = $array2[$ptr2++];
}
}
// Merge the remainder
while ($ptr1 < count($array1)) {
$array[] = $array1[$ptr1++];
}
while ($ptr2 < count($array2)) {
$array[] = $array2[$ptr2++];
}
return;
}