验证银行卡位数和正确性

public function check_bankCard($card_number){
    
    $arr_no = str_split($card_number);
   
    $last_n = $arr_no[count($arr_no)-1];
  
    krsort($arr_no);
   
   $i = 1;
   
   $total = 0;
 
   foreach ($arr_no as $n){
 
       if($i%2==0){
       
             $ix = $n*2;
      
              if($ix>=10){
    
                    $nx = 1 + ($ix % 10);
  
                      $total += $nx;
           
            }else{
              
             $total += $ix;
        
                }
     
      }else{
      
          $total += $n;
   
         }
   
         $i++;
  
   }
 
   $total -= $last_n;
  
   $x = 10 - ($total % 10);
  
   if($x == $last_n){
       return 'true';
   
   }else{
    
       return 'false';
 
  }
}

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