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.
bcmul
(PHP 4, PHP 5, PHP 7, PHP 8)
bcmul — Multiplica dos números de precisión arbitraria
Descripción
Multiplica el left_operand por el
right_operand.
Parámetros
-
left_operand -
El left operand, como una cadena.
-
right_operand -
El right operand, como una cadena.
-
scale -
Este parámetro opcional es usado para establecer el número de dígitos después del punto decimal en el resultado. Si se omite, su valor será el de la escala establecida globalmente con la función bcscale(), o se recurrirá a
0si este valor no ha sido establecido.
Valores devueltos
Devuelve el resultado como una cadena.
Ejemplos
Ejemplo #1 Ejemplo bcmul()
<?php
echo bcmul('1.34747474747', '35', 3); // 47.161
echo bcmul('2', '4'); // 8
?>
add a note
User Contributed Notes 4 notes
Nitrogen ¶
15 years ago
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',$float1), 32);
//0.000000000000000000000000000000015617072071671;
?>
admin at spamhere dot sinfocol dot org ¶
13 years ago
Well, I have a little problem implementing Blake Hash in my server because it is not a x64 server machine. I made a little function that use the powerfull of BC library to do the bitwise operation Shift.
<?php
echo 'Left Shift test<br />';
bprint('1', decbin(1));
bprint('1 << 32 (Fail)', decbin(1 << 32)); //Fail, operation not succesfull in 32-bit machine
bprint('shiftleft(1, 32) (Success)', dec2bin(shiftleft('1', '32'))); //decbin fails, so we use personalized function, success
echo '<br />';
echo 'Right Shift test<br />';
bprint('9223372036854775808', dec2bin('9223372036854775808'));
bprint('9223372036854775808 >> 63 (Fail)', decbin(9223372036854775808 >> 63));
bprint('rightshift(9223372036854775808, 63) (Success)', decbin(rightshift('9223372036854775808', '63')));
function shiftleft($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;
}
?>
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.
