Quicksort PHP SplFixedArray in PHP5.6, based on a key

quickSortPHPSplFixedArray

    /**
     * Quicksorting (with partition) implementation to sort SplFixedArray on a specific key, 
     * I could not find this and I needed this because I'm stuck on PHP5.6 at work -- 2023-05-04 wuhei
     *
     * @param $arr SplFixedArray, array to sort
     * @param $key mixed, array key to sort on
     * @param $desc bool if true, sort descending
     * @param $leftIndex int, left index of the array to sort, defaults to 0
     * @param $rightIndex int, right index of the array to sort, defaults to count($arr) - 1
     * @return mixed
     * @throws Exception, if you forgot something useful
     * @author 2023-05-04 wuhei
     */
    public function quickSort(&$arr = NULL, $key = NULL, $desc = NULL, $leftIndex, $rightIndex) {
        if(NULL === $arr) {
            throw new Exception("No SplFixedArray provided");
        }
        if(NULL === $key) {
            throw new Exception("Nessun key to order on provided");
        }
        if($desc !== true) {
            $desc = false;
        }
        // single element array, return and done
        if(count($arr) <= 1) {
            return $arr;
        }
        if(NULL === $leftIndex) {
            $leftIndex = 0;
        }
        if(NULL === $rightIndex) {
            $rightIndex = count($arr) - 1;
        }
        if($leftIndex < $rightIndex) {
            $pivot = $this->partition($arr, $key, $leftIndex, $rightIndex);
            quickSort($arr, $key, NULL, $leftIndex, $pivot - 1);
            quickSort($arr, $key, NULL, $pivot + 1, $rightIndex);
        }
        if($desc) {
            // reverse the array
            $l = $arr->count();
            $reverseArr = new SplFixedArray($l);
            $z = 0;
            for($i=$l-1;$i>=0;$i--) {
                $reverseArr[$z] = $arr[$i];
                $z++;
            }
            $arr = $reverseArr;
        }
        return $arr;
    }
    
    public function partition(&$arr = NULL,$key = NULL, $leftIndex = NULL ,$rightIndex = NULL) {
        if(NULL === $arr) {
            throw new Exception("no SplFixedArray given");
        }
        if(NULL === $key) {
            throw new Exception("no key to order on provided");
        }
        $pivot = &$arr[$rightIndex];
        $i = $leftIndex;
        for($j=$leftIndex;$j<$rightIndex;$j++) {
            if($arr[$j][$key] <= $pivot[$key]){
                $tmp = $arr[$i];
                $arr[$i] = $arr[$j];
                $arr[$j] = $tmp;
                $i++;
            }
        }
        $tmp = $arr[$i];
        $arr[$i] = $arr[$rightIndex];
        $arr[$rightIndex] = $tmp;
        return $i;
    }