<?php
  function add($summand, $addend)
  {
    $sum = $summand ^ $addend;
    // 判斷進(jìn)位
    $carry = $summand & $addend;
    while ($carry <<= 1) {
      $summand = $sum;
      $addend = $carry;
      $sum = $summand ^ $addend;
      $carry = $summand & $addend;
    }
    return $sum;
  }

<?php
  require 'addition.php';

  function subtract($minuend, $subtrahend)
  {
    // 先求得減數(shù)的補(bǔ)碼，然后求和
    $subtrahend = add(~$subtrahend, 1);

    return add($minuend, $subtrahend);
  }

<?php  require 'addition.php';
  function multiply($multiplicand, $multiplicator)
  {
    // 判斷符號位
    $flag = ($multiplicand ^ $multiplicator) < 0 ? false : true;
    // 被乘數(shù)和乘數(shù)取絕對值
    $multiplicand = $multiplicand < 0 ? add(~$multiplicand, 1) : $multiplicand;
    $multiplicator = $multiplicator < 0 ? add(~$multiplicator, 1) : $multiplicator;
    $product = 0;
    $multiplicator = decbin($multiplicator);
    $length = strlen($multiplicator);
    for ($i = 0; $i < $length; $i ++) {
      if ($multiplicator[$i]) {
        $product += $multiplicand << $length - $i - 1;
      }
    }
    if (! $flag) {
      $product = add(~$product, 1);
    }
    return $product;
  }

<?php
  require 'addition.php';

  function divide($dividend, $divisor)
  {
    // 判斷符號位
    $flag = ($dividend ^ $divisor) < 0 ? false : true;
    // 取得被除數(shù)符號位
    $dividend_flag = $dividend < 0 ? false : true;
    // 取絕對值
    $dividend = $dividend < 0 ? add(~$dividend, 1) : $dividend;
    $divisor = $divisor < 0 ? add(~$divisor, 1) : $divisor;

    $quotient = 0;
    $remainder = 0;

    if ($dividend < $divisor) {
      // 被除數(shù)小于除數(shù)的情況
      $remainder = $dividend;
      return 'quotient = ' . $quotient . ' remainder = ' . $remainder;
    }

    while ($dividend >= $divisor) {
      $i = 0;
      $mul_divisor = $divisor;

      while ($dividend >= ($mul_divisor << 1)) {
        $i ++;
        $mul_divisor <<= 1;
      }

      $dividend -= $mul_divisor;
      $quotient += 1 << $i;
    }

   $remainder = $dividend;
   if (! $flag) {
     $quotient = add(~ $quotient, 1);
   }
   if (! $dividend_flag) {
     $remainder = add(~$remainder, 1);
   }

   return 'quotient = ' . $quotient . ' remainder = ' . $remainder;
  }