Переменная Sass в функции CSS calc ()

Ниже приведен класс для реализации Quick Sort в PHP -

            <?php
            class quickSort{
            /* low  --> Starting index,  high  --> Ending index */
                public $arr;
                public function __construct($arr){
                    $this->arr = $arr;
                }
                public function qsort($low,$high){
                    if($low===null || $high===null){    
                        return false;
                    }
                    if($low < $high){           
                        $pi = $this->partition($low,$high);
                        $this->qsort($low,$pi-1); /*before pivot*/
                        $this->qsort($pi+1,$high); /*before pivot*/
                    }
                }

                /* This function takes last element as pivot, places
                   the pivot element at its correct position in sorted
                    array, and places all smaller (smaller than pivot)
                   to left of pivot and all greater elements to right
                   of pivot */
                public function partition($low,$high){
                    if($low===null || $high===null){
                        return false;
                    }
                    $pivot = $this->arr[$high];
                    $i = $low-1; /*index of smaller element*/

                    for($j = $low; $j <= $high-1; $j++)
                    {
                        // If current element is smaller than or equal to pivot

                        if($this->arr[$j] <= $pivot)
                        {
                            $i++;    // increment index of smaller element
                            $this->swap($i,$j);         
                        }
                    }
                    //swap arr[i + 1] and arr[high])
                    $this->swap($i+1,$high);

                    return $i+1;    
                }

                public function swap($i,$j){
                    $p=$this->arr[$i];
                    $q=$this->arr[$j];
                    $this->arr[$i]=$q;
                    $this->arr[$j]=$p;      
                }
            }
            $arr = array(10, 80, 30, 90, 40, 50, 70);
            $obj = new quickSort($arr);
            $obj->qsort(0,6);
            print_r($obj->arr);


            ?>