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bcmul

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

bcmul2つの任意精度数値の乗算を行う

説明

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

num1num2 を掛けます。

パラメータ

num1

左オペランドを表す文字列。

num2

右オペランドを表す文字列。

scale
This parameter is used to set the number of digits after the decimal place in the result. If null, it will default to the default scale set with bcscale(), or fallback to the value of the bcmath.scale INI directive.

戻り値

結果を文字列で返します。

エラー / 例外

This function throws a ValueError in the following cases:

  • num1 or num2 is not a well-formed BCMath numeric string.
  • scale is outside the valid range.

変更履歴

バージョン 説明
8.0.0 scale は、nullable になりました。
7.3.0 bcmul() 関数が、指定されたスケールの数値を返すようになりました。 これより前のバージョンでは、 返される数値の末尾が 0埋め されることなく、省略される可能性がありました。

例1 bcmul() の例

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

注意

注意:

PHP 7.3.0 より前のバージョンでは、 bcmul()scale 引数で指定したものより少ない桁数を返す可能性がありました。 これは scale で許された精度が不要な場合にだけ起きていました。 たとえば、以下のような場合です:

例2 bcmul() で scale を指定する例

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

参考

  • bcdiv() - 2つの任意精度数値で除算を行う

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User Contributed Notes 4 notes

up
10
Nitrogen
15 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.
up
7
mgkirs
7 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;
?>
up
4
admin at spamhere dot sinfocol dot org
13 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;
}
?>
up
0
gar37bic at gmail dot com
12 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.
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