bcmul

(PHP 4, PHP 5)

bcmul — 두 임의 정밀도 수 곱하기

설명

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

left_operand 를 right_operand 로 곱합니다.

인수

left_operand: 왼쪽 연산수, 문자열.
right_operand: 오른쪽 연산수, 문자열.
scale: 이 선택적인 인수는 소수점 아래 자리수를 설정합니다. bcscale()을 사용하여 모든 함수에 대한 전역 기본값을 설정할 수 있습니다.

반환값

결과를 문자열로 반환합니다.

예제

Example #1 bcmul() 예제


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

참고

bcdiv() - 두 임의 정밀도 수 나누기

bcpow

bcmod

Last updated: Fri, 24 Jul 2009

add a note User Contributed Notes
bcmul

Nitrogen
09-Jul-2009 09:55


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.

ju(...)
02-Apr-2008 05:00


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).

xpheas (at) gmail . com
15-Jun-2007 12:13


if you have compiled php width "--disable-bcmath", you can use this:



<?php

  function bcmul($_ro, $_lo, $_scale=0)

  {

    return round($_ro*$_lo, $_scale);

  }

?>

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bcpow

bcmod

Last updated: Fri, 24 Jul 2009