大数字 大数值 溢位数值 加减运算 算法

<?php

   $a = "9999888877776666555544443333322222111110000000000000000000000000000";
   $b = "1000236540001";

   //计算两字符串长度，并获取最长字符串长度
   $a_len = mb_strlen($a);
   $b_len = mb_strlen($b);
   $a_len >= $b_len ? $total_len =$a_len:$total_len = $b_len;

   //将两串字符串补全到最长字符串长度，左边以字符串"0"补全
   $a_new = str_pad($a,$total_len,'0',STR_PAD_LEFT);
   $b_new = str_pad($b,$total_len,'0',STR_PAD_LEFT);

   //将两字符串 按照字符单元拆分，分别存储到对应的数组当中
   $a_str_array = array();
   $b_str_array = array();
   for($i=$total_len-1;$i>=0;$i--){
       $target_str_a = "";
       $target_str_b = "";
       $target_str_a = mb_substr($a_new,$i,1);

       $target_str_b = mb_substr($b_new,$i,1);
       $a_str_array[] = $target_str_a;
       $b_str_array[] = $target_str_b;
   }
   //如上循环可换做str_split()改写  例：$c_array= str_split("Shanghai",3)
  $new_combine_array = array();

  //循环上面的数组 按相同索引对应元素值进行数值加减运算（如果是减法法则需要从高位往低位运算，如果是加法则需要从低位往高位运算），并进行进位处理，然后将运算值存储到新的数组当中
  for($n=0;$n<=$total_len;$n++){
    $n_digit = intval($a_str_array[$n])+intval($b_str_array[$n]);
    if($n_digit>=10){
        //如果当前位两数值相加大于等于10 ，则需要进位，处理办法是任选一个之前的拆分数组$a_str_array 或 $b_str_array,将其第$n+1个元素加1（有可能使该元素值等于10）
        $n_digit = $n_digit-10;
            //$n_digit -= 10;
        $a_str_array[$n+1] = strval(intval($a_str_array[$n+1])+1);
    }
    $new_combine_array[$n] = $n_digit;
  }

  //将拆分运算后的数组进行拆分拼接
  $new_combine_str = "";
  $new_combine_array_length = count($new_combine_array);
  for($m=$new_combine_array_length-1;$m>=0;$m--){
      //判断最高位字符串是否为"0"，若为"0"则不拼接
      $m ==$new_combine_array_length-1 && $new_combine_array[$new_combine_array_length-1]=="0"?$new_combine_str = $new_combine_str:$new_combine_str .= $new_combine_array[$m];
  }

 echo $new_combine_str;


?>

方法二：

function big_number($num1,$num2){
   $num1 = rtrim($num1,"0");
   $num1 = rtrim($num1,".");
   $num2 = rtrim($num2,"0");
   $num2 = rtrim($num2,".");
   $len1 = strlen($num1);
   $len2 = strlen($num2);
   $diff1 =  $len1 - (strpos($num1,".")?:$len1);
   $diff2 =  $len2 - (strpos($num2,".")?:$len2);
   $char_index1 = strpos($num1,".")?:$len1;
   $char_index2 = strpos($num2,".")?:$len2;
   $diff = abs($diff1 - $diff2);
   $char_index = $diff1 > $diff2 ? $diff1 : $diff2;
   if($diff1 > $diff2){
      $num2 = str_pad($num2,$len2 + $diff,"0",STR_PAD_RIGHT);
   }else{
      $num1 = str_pad($num1,$len1 + $diff,"0",STR_PAD_RIGHT);
   }

   $num1 = str_replace(".","",$num1);
   $num2 = str_replace(".","",$num2);
   $len1 = strlen($num1);
   $len2 = strlen($num2);
   $len = $len1 > $len2 ? $len1 : $len2;
   $num1 = str_pad($num1,$len,"0",STR_PAD_LEFT);
   $num2 = str_pad($num2,$len,"0",STR_PAD_LEFT);
   $arr1 = str_split($num1);
   $arr2 = str_split($num2);
   $arr = [];
   $mod = 0;
   for($i = $len - 1;$i >= 0;$i--){
      $num = (int)$arr1[$i] + (int)$arr2[$i] + $mod;
      if($num >= 10){
         $num -= 10;
         $mod = 1;
      }else{
         $mod = 0;
      }
      array_unshift($arr,$num);
   }
   $num = implode("",$arr);
   if($char_index > 0){
      $num = substr($num,0,strlen($num) - $char_index + 1).".".substr($num,1 - $char_index);
      $num = rtrim($num,"0");
      $num = rtrim($num,".");
   }
   return $num;
}
$num1 = "1423547535454.34859347895";
$num2 = "543789538243290874093.545";
$num = big_number($num1,$num2);
echo $num;