<?php

function reverse_comp_func($n1,$n2) {
  $n1=(int)$n1; $n2=(int)$n2;
  return $n1 === $n2 ? 0 : ($n1 > $n2 ? -1 : 1);
}

$a = array(3, 2, 5, 6, 10);
usort($a, "reverse_comp_func");
var_dump($a);