PHP - Manual: bcmul

2024-12-21

bcpow »

« bcmod

bcmul

(PHP 4, PHP 5, PHP 7, PHP 8)

bcmul — 两个任意精度数字乘法计算

说明

bcmul(string $num1, string $num2, ?int $scale = null): string

num1 乘以 num2。

参数

num1: 字符串类型的左操作数。
num2: 字符串类型的右操作数。
scale: 此可选参数用于设置结果中小数点后的小数位数。也可通过使用 bcscale() 来设置全局默认的小数位数，用于所有函数。如果未设置，则默认为 0。

返回值

返回字符串类型的结果。

更新日志

版本	说明
8.0.0	现在 `scale` 可以为 null。
7.3.0	现在 bcmul() 可以按想要的小数点位数返回数字。而之前，返回的数字会忽略尾随零（trailing decimal zeroes）。

范例

示例 #1 bcmul() 示例


<?php
echo bcmul('1.34747474747', '35', 3); // 47.161
echo bcmul('2', '4'); // 8
?>

注释

注意:
Before PHP 7.3.0 bcmul() may return a result with fewer digits after the decimal point than the scale parameter would indicate. This only occurs when the result doesn't require all of the precision allowed by the scale. For example:

示例 #2 bcmul() scale example

<?php echo bcmul('5', '2', 2); // prints "10", not "10.00" ?>

参见

bcdiv() - 两个任意精度的数字除法计算

add a note

User Contributed Notes 4 notes

down

mgkirs ¶

4 years ago


$float = 0.31234144143341;
$float1 = 0.00000000000000000000000000000005;
echo $float, "\n";
//0.31234144143341
echo $float1, "\n";
//5.0E-32
echo $float*$float1, "\n";
//1.5617072071671E-32

<?php
/*bcmul read float as string*/
echo bcmul($float, $float1, 32),"\n";
//0
echo bcmul($float, sprint('%.32f',$float1), 32);
//0.000000000000000000000000000000015617072071671;
?>

down

Nitrogen ¶

12 years ago


I made this to multiply an unlimited size of integers together (meaning no decimals)..
This could be useful for those without the BCMath extension.

<?php

function Mul($Num1='0',$Num2='0') {
  // check if they're both plain numbers
  if(!preg_match("/^\d+$/",$Num1)||!preg_match("/^\d+$/",$Num2)) return(0);

  // remove zeroes from beginning of numbers
  for($i=0;$i<strlen($Num1);$i++) if(@$Num1{$i}!='0') {$Num1=substr($Num1,$i);break;}
  for($i=0;$i<strlen($Num2);$i++) if(@$Num2{$i}!='0') {$Num2=substr($Num2,$i);break;}

  // get both number lengths
  $Len1=strlen($Num1);
  $Len2=strlen($Num2);

  // $Rema is for storing the calculated numbers and $Rema2 is for carrying the remainders
  $Rema=$Rema2=array();

  // we start by making a $Len1 by $Len2 table (array)
  for($y=$i=0;$y<$Len1;$y++)
    for($x=0;$x<$Len2;$x++)
      // we use the classic lattice method for calculating the multiplication..
      // this will multiply each number in $Num1 with each number in $Num2 and store it accordingly
      @$Rema[$i++%$Len2].=sprintf('%02d',(int)$Num1{$y}*(int)$Num2{$x});

  // cycle through each stored number
  for($y=0;$y<$Len2;$y++)
    for($x=0;$x<$Len1*2;$x++)
      // add up the numbers in the diagonal fashion the lattice method uses
      @$Rema2[Floor(($x-1)/2)+1+$y]+=(int)$Rema[$y]{$x};

  // reverse the results around
  $Rema2=array_reverse($Rema2);

  // cycle through all the results again
  for($i=0;$i<count($Rema2);$i++) {
    // reverse this item, split, keep the first digit, spread the other digits down the array
    $Rema3=str_split(strrev($Rema2[$i]));
    for($o=0;$o<count($Rema3);$o++)
      if($o==0) @$Rema2[$i+$o]=$Rema3[$o];
      else @$Rema2[$i+$o]+=$Rema3[$o];
  }
  // implode $Rema2 so it's a string and reverse it, this is the result!
  $Rema2=strrev(implode($Rema2));

  // just to make sure, we delete the zeros from the beginning of the result and return
  while(strlen($Rema2)>1&&$Rema2{0}=='0') $Rema2=substr($Rema2,1);

  return($Rema2);
}

$A='5650175242508133742';
$B='2361030539975818701734615584174625';

printf("  Mul(%s,%s); // %s\r\n",$A,$B,  Mul($A,$B));
printf("BCMul(%s,%s); // %s\r\n",$A,$B,BCMul($A,$B)); // build-in function

/*
  This will print something similar to this..
    Mul(5650175242508133742,2361030539975818701734615584174625);
  BCMul(5650175242508133742,2361030539975818701734615584174625);

  both of which should be followed by the answer:
  13340236303776981390475700774516825287352418182696750
*/

?>

It was a fun experience making.. even though this took me longer than the BCAdd alternative I did..
Memory allocation might be an issue for rediculously larger numbers though.. if someone wants to benchmark the performance of my function; feel free.
Enjoy,
Nitrogen.

down

admin at spamhere dot sinfocol dot org ¶

11 years ago


Well, I have a little problem implementing Blake Hash in my server because it is not a x64 server machine. I made a little function that use the powerfull of BC library to do the bitwise operation Shift.

<?php
echo 'Left Shift test<br />';
bprint('1', decbin(1));
bprint('1 << 32 (Fail)', decbin(1 << 32)); //Fail, operation not succesfull in 32-bit machine
bprint('shiftleft(1, 32) (Success)', dec2bin(shiftleft('1', '32'))); //decbin fails, so we use personalized function, success

echo '<br />';
echo 'Right Shift test<br />';
bprint('9223372036854775808', dec2bin('9223372036854775808'));
bprint('9223372036854775808 >> 63 (Fail)', decbin(9223372036854775808 >> 63));
bprint('rightshift(9223372036854775808, 63) (Success)', decbin(rightshift('9223372036854775808', '63')));

function shiftleft($num, $bits) {
    return bcmul($num, bcpow('2', $bits));
}

function rightshift($num, $bits) {
    return bcdiv($num, bcpow('2', $bits));
}

function bprint($title, $content) {
    echo $title . '<br />' . str_pad($content, 64, '0', STR_PAD_LEFT) . '<br />' . PHP_EOL;
}

//http://www.php.net/manual/en/function.decbin.php#99533
function dec2bin($dec) {
    // Better function for dec to bin. Support much bigger values, but doesn’t support signs
    for ($b = '', $r = $dec; $r >1;) {
        $n = floor($r / 2);
        $b = ($r - $n * 2) . $b;
        $r = $n; // $r%2 is inaccurate when using bigger values (like 11.435.168.214)!
    }
    return ($r % 2) . $b;
}
?>

down

gar37bic at gmail dot com ¶

9 years ago


When using printf to print the results of bcmath operations, use string format, i.e. '%s', not numeric formats such as '%d' or '%f'.  For example, the output of factorial (23) will be incorrect if using %d or %f:

Result using %f:
factorial (22) = 1124000727777607680000 (correct)
factorial (23) = 25852016738884978212864 (incorrect)

Result using %s:
factorial (22) = 1124000727777607680000
factorial (23) = 25852016738884976640000

Using echo, this is not a problem - PHP will output the bcmath string type correctly.

add a note

官方地址：https://www.php.net/manual/en/function.bcmul.php

有任何技术问题请点击这里网站运营推广招聘

IT PHP 编程语言 Linux 开发编程科技 Elasticsearch HTML/CSS/XML 网络数据库 JAVA 面试 NoSQL C/C++ Golang Git 算法操作系统正则表达式 Redis 互联网 MySql JavaScript 运维软件国际架构设计 Mac OS TCP/IP Excel Vim Windows Socket Oracle VR MongoDB Python 运营 MemCache 商业硬件电子娱乐设计 nginx 摄影游戏 WordPress HTTP 团建数码电器

php7 安装fileinfo扩展 preg_split — 通过一个正则表达式分隔字符串 php位值,解决 PHP 中 usort 在值相同时改变原始位置的问题 [PHP] inet_pton/inet_ntop IP地址转换函数 PHP 8.1 [鸟哥]PHP_INT_MIN 和 -9223372036854775808 adodb手册 ADORecordSet对象 opcache预加载 Composer的Packagist资源 array_multisort() 多字段排序 PHPMailer设置utf8 PHPMailer字符集CharSet mysql面试题 PHP json解析（json_decode）页面工具纯php实现DES以及TripleDES加密算法 [原创]诡异的php-fpm超时问题 Packagist / Composer 中国全量镜像 php中几种注释规范 php 修改图片大小两千行PHP学习笔记

略微加速

PHP官方手册 - 互联网笔记

bcmul

说明

参数

返回值

更新日志

范例

注释

参见

User Contributed Notes 4 notes