multiplication.php

<?php
/*****************************************************************************
 *         In the name of God the Most Beneficent the Most Merciful          *
 *___________________________________________________________________________*
 *   This program is free software: you can redistribute it and/or modify    *
 *   it under the terms of the GNU General Public License as published by    *
 *   the Free Software Foundation, either version 3 of the License, or       *
 *   (at your option) any later version.                                     *
 *___________________________________________________________________________*
 *   This program is distributed in the hope that it will be useful,         *
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of          *
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the           *
 *   GNU General Public License for more details.                            *
 *___________________________________________________________________________*
 *   You should have received a copy of the GNU General Public License       *
 *   along with this program.  If not, see <http://www.gnu.org/licenses/>.   *
 *___________________________________________________________________________*
 *                       Created by AliReza Ghadimi                          *
 *     <http://AliRezaGhadimi.ir>    LO-VE    <AliRezaGhadimy@Gmail.com>     *
 *****************************************************************************/

/**
 * @param $a
 * @param $b
 * @return string
 */
function big_sum($a,$b){
    $a          = (string)$a;
    $b          = (string)$b;
    $big        = strlen($a) > strlen($b) ? strlen($a) : strlen($b);
    $a          = str_split(str_pad($a,$big,"0",STR_PAD_LEFT),5);
    $b          = str_split(str_pad($b,$big,"0",STR_PAD_LEFT),5);
    $return     = "";
    $remind     = 0;
    $count      = count($a)-1;
    for($i = $count;$i >= 0;$i--){
        $f  = strlen($a[$i]);
        $s  = (string)((int)$a[$i]+(int)$b[$i]+$remind);
        $sl = strlen($s);
        if($sl > $f){
            $p      = $sl-$f;
            $remind = (int)(substr($s,0,$p));
            $s      = (string)(substr($s,$p,$sl));
        }else{
            $remind = 0;
        }
        $return = $s.$return;
    }
    $_return    = $remind !== 0 ? (string)$remind : "";
    return $_return.$return;
}

/**
 * @param $a
 * @param $b
 * @return int|string
 */
function big_multiplication($a,$b){
    $a          = (string)$a;
    $b          = (string)$b;

    $big     = strlen($a) > strlen($b) ? $a : $b;
    $small   = strlen($b) >= strlen($a) ? $a : $b;

    $f       = 1;
    $small   = str_split($small,$f);
    $big     = str_split($big,$f);

    $count      = count($small)-1;
    $count_b    = count($big)-1;
    $remind     = 0;
    $return     = 0;
    for($i = $count;$i >= 0;$i--){
        $p  = "";
        $iS = (int)$small[$i];
        for($j = $count_b;$j >= 0;$j--){
            $iB = (int)$big[$j];
            $s  = (string)(($iS*$iB)+$remind);
            $sl = strlen($s);
            if($sl > $f){
                $l      = $sl-$f;
                $remind = (int)(substr($s,0,$l));
                $s      = (string)(substr($s,$l,$sl));
            }else{
                $remind = 0;
            }
            $p  = ((string)$s).$p;
        }
        $return = big_sum($return,($remind !== 0 ? (string)$remind : "").$p.str_repeat("0",$count-$i));
        $remind = 0;
    }
    return $return;
}