<?php
class calculator {
    
    /**
     * Variable for holding all the numbers to add
     *
     * @var array
     */
    private $numbers = array();
    
    /**
     * Variable holding all the digits after the point
     *
     * @var array
     */
    private $afterPoint = array();
    
    /**
     * Maximum number of digits after the point
     * that a number has
     *
     * @var int
     */
    private $afterPointLength = 0;
    
    /**
     * Final result
     *
     * @var string
     */
    private $result = 0;
    
    /**
     * Constructor
     *
     */
    public function __construct() {
        
    }
    
    /**
     * Adds a number to the list of numbers
     * to be summed
     *
     * @param string $number
     */
    public function addNumber ($number) {
        $this->numbers[] = (string)$number;
    }
    
    /**
     * Adds two numbers
     *
     * @param string $n1
     * @param string $n2
     * @return string
     */
    private function doAdd ($n1, $n2) {
        
        if ($n1 == 0) return $n2;
        if ($n2 == 0) return $n1;
        
        if (strlen($n1) <=13 && strlen($n2) <= 13) {
            return (string)$n1+$n2;
        }
        
        $finalNumber = array();
        $c = 0;
        
        $n1 = (string)$n1;
        $n2 = (string)$n2;
        
        $m = max(strlen($n1), strlen($n2));
        $n1 = str_pad($n1, $m, " ", STR_PAD_LEFT);
        $n2 = str_pad($n2, $m, " ", STR_PAD_LEFT);
        
        $numbers1 = chunk_split($n1, 13, ";");
        $numbers1 = substr($numbers1, 0, -1);
        $numbers1 = explode(";", $numbers1);
        $numbers1 = array_reverse($numbers1);
        
        $numbers2 = chunk_split($n2, 13, ";");
        $numbers2 = substr($numbers2, 0, -1);
        $numbers2 = explode(";", $numbers2);
        $numbers2 = array_reverse($numbers2);
        
        $maxSize = max(count($numbers1), count($numbers2));
        
        for ($i=0;$i<$maxSize;$i++) {
            
            $totalZeros  = 0;
            $totalZeros1 = 0;
            $totalZeros2 = 0;
            for ($j=0;$j<strlen($numbers1[$i]);$j++) {
                if ($numbers1[$i][$j] == 0) {
                    $totalZeros1++;
                } else {
                    break;
                }
            }
            
            for ($j=0;$j<strlen($numbers1[$i]);$j++) {
                if ($numbers2[$i][$j] == 0) {
                    $totalZeros2++;
                } else {
                    break;
                }
            }
            
            $totalZeros = max($totalZeros1, $totalZeros2);
            
            $partialResult = (string)($numbers1[$i] + $numbers2[$i] + $c);
            $partialResult = str_pad($partialResult, strlen($partialResult)+$totalZeros, "0", STR_PAD_LEFT);
            if (strlen($partialResult) > max(strlen($numbers1[$i]),strlen($numbers2[$i]))) {
                $partialResult = (string)$partialResult;
                $c = $partialResult[0];
                $finalNumber[] = substr($partialResult, 1);
            } else {
                $c=0;
                $finalNumber[] = $partialResult;
            }
        }
        $finalNumber = array_reverse($finalNumber);
        $finalNumber = implode("", $finalNumber);
        if ($c != 0) $finalNumber = $c.$finalNumber;
        return $finalNumber;
    }
    
    /**
     * Make the calculation
     *
     * @return string
     */
    public function calc () {
        
        for ($i=0; $i<count($this->numbers);$i++) {
            $n = explode(".", $this->numbers[$i]);
            if (count($n) == 1) {
                $this->result = $this->doAdd($this->result, $this->numbers[$i]);
            } elseif (count($n) == 2) {
                $this->afterPoint[] = $n[1];
                $this->afterPointLength = max($this->afterPointLength, strlen($n[1]));
                $this->result = $this->doAdd($this->result, $n[0]);
            } else {
                trigger_error("<b>".$this->numbers[$i]."</b> is invalid !!", E_USER_ERROR);
            }
        }
        
        if ($this->afterPointLength > 0) {
            $r = 0;
            foreach ($this->afterPoint as $number) {
                $number = str_pad($number, $this->afterPointLength, "0", STR_PAD_RIGHT);
                $r = $this->doAdd($r, $number);
            }
            if (strlen($r) > $this->afterPointLength) {
                $this->result = $this->doAdd($this->result, substr($r, 0, -$this->afterPointLength));
                if (strrpos($r, "0") != strlen($r)-1)
                    $this->result = $this->result.".".substr($r, 1);
            } else {
                $this->result = $this->result.".".$r;
            }
        }
        return $this->result;
    }
}


// example
$calc = new calculator();
// generate a very big numer
$number  = "8347610948712974071265710983243861208762139437204172409821378273618976529283
476109487129740712657109";
$number = str_repeat($number, 10000);


$calc->addNumber($number);
$calc->addNumber($number);

$time_start = microtime(true);
$result = $calc->calc();
$time_end = microtime(true);

print "\nThe number has ".strlen($number)." digits. ";
print "\nThe result has ".strlen($result)." digits. ";

print "\nThe result is: ".$result;


print "\nThe sum was executed in ".($time_end-$time_start)." seconds.";

?>