bcmul

(PHP 4, PHP 5, PHP 7)

bcmul — 2个任意精度数字乘法计算

说明

string bcmul ( string $left_operand , string $right_operand [, int $scale = int ] )

左操作数乘以右操作数

参数

left_operand: 字符串类型的左操作数.
right_operand: 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。

返回值

返回结果为字符串类型.

范例

Example #1 bcmul() 示例

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

参见

bcdiv() - 2个任意精度的数字除法计算

用户评论:

[#1] gar37bic at gmail dot com [2012-11-19 17:06:20]

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.

[#2] admin at spamhere dot sinfocol dot org [2011-01-03 22:17:01]

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; } ?>

[#3] Nitrogen [2009-07-08 17:55:37]

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 ?>

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.

[#4] ju(...) [2008-04-02 00:00:54]

Except that with xpheas method, you lose all the benefits of arbitrary precision as the * operator only works on int and float and those are restricted in length (See int ant float types for more information).