Edit Report a Bug

bcmul

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

bcmul — Multiplie deux nombres de grande taille

Description

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

Multiplie l'opérande num1 par l'opérande num2.

Liste de paramètres

num1: L'opérande de gauche, sous la forme d'une chaîne de caractères.
num2: L'opérande de droite, sous la forme d'une chaîne de caractères.
scale: Ce paramètre optionnel est utilisé pour définir le nombre de chiffres après la décimale à placer dans le résultat. Vous pouvez également définir la précision globale par défaut pour toutes les fonctions en utilisant la fonction bcscale().

Valeurs de retour

Retourne le résultat, sous la forme d'une chaîne de caractères.

Historique

Version	Description
8.0.0	`scale` est désormais nullable.
7.3.0	bcmul() retourne désormais les nombres avec la précision demandé. Auparavant, les nombres retournés pouvait omettre les zéros décimaux trainant à la fin.

Exemples

Exemple #1 Exemple avec bcmul()

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

Notes

Note:
Antérieur à PHP 7.3.0 bcmul() peut retourner un résultat avec moins de chiffres après la virgule que le parmètre scale indique. Ceci ne se produit que le résultat ne nécessite pas toute la précision autorisée par scale. Par exemple:

Exemple #2 bcpow() exemple pour scale

<?php echo bcmul('5', '2', 2); // affiche "10", pas "10.00" ?>

Voir aussi

bcdiv() - Divise deux nombres de grande taille

add a note

User Contributed Notes 4 notes

down

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.

down

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;
?>

down

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;
}
?>

down

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.

add a note