PHP 5.4.31 Released

bcmul

(PHP 4, PHP 5)

bcmulMultiply two arbitrary precision numbers

Descrierea

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

Multiply the left_operand by the right_operand.

Parametri

left_operand

The left operand, as a string.

right_operand

The right operand, as a string.

scale

Acest parametru opțional este utilizat pentru a stabili numărul cifrelor după virgulă din rezultat. De asemenea puteți să stabiliți parametrul global scale pentru toate funcțiile utilizând bcscale().

Valorile întoarse

Returns the result as a string.

Exemple

Example #1 bcmul() example

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

Vedeți de asemenea

  • bcdiv() - Divide two arbitrary precision numbers

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User Contributed Notes 4 notes

up
2
Nitrogen
5 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",$A,$BMul($A,$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
1
gar37bic at gmail dot com
1 year 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.
up
0
admin at spamhere dot sinfocol dot org
3 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
-1
ju(...)
6 years ago
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).
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