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bcpow

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

bcpowRaise an arbitrary precision number to another

Description

bcpow(string $num, string $exponent, ?int $scale = null): string

Raise num to the power exponent.

Parameters

num

The base, as a string.

exponent

The exponent, as a string. If the exponent is non-integral, it is truncated. The valid range of the exponent is platform specific, but is at least -2147483648 to 2147483647.

scale

This optional parameter is used to set the number of digits after the decimal place in the result. If omitted, it will default to the scale set globally with the bcscale() function, or fallback to 0 if this has not been set.

Return Values

Returns the result as a string.

Changelog

Version Description
7.3.0 bcpow() now returns numbers with the requested scale. Formerly, the returned numbers may have omitted trailing decimal zeroes.

Examples

Example #1 bcpow() example

<?php

echo bcpow('4.2', '3', 2); // 74.08

?>

Notes

Note:

Before PHP 7.3.0 bcpow() may return a result with fewer digits after the decimal point than the scale parameter would indicate. This only occurs when the result doesn't require all of the precision allowed by the scale. For example:

Example #2 bcpow() scale example

<?php
echo bcpow('5', '2', 2); // prints "25", not "25.00"
?>

See Also

  • bcpowmod() - Raise an arbitrary precision number to another, reduced by a specified modulus
  • bcsqrt() - Get the square root of an arbitrary precision number

add a note

User Contributed Notes 3 notes

up
-1
Michael Bailey (jinxidoru at byu dot net)
19 years ago
bcpow() only supports exponents less than or equal to 2^31-1. Also, bcpow() does not support decimal numbers. If you have scale set to 0, then the exponent is converted to an interger; otherwise an error is generated.

--
Michael Bailey
http://www.jinxidoru.com
up
-2
thomas at tgohome dot com
14 years ago
<?php

bcscale
(100);

/*
* Computes the natural logarithm using a series.
* @author Thomas Oldbury.
* @license Public domain.
*/
function bcln($a, $iter = 10)
{
$result = "0.0";

for(
$i = 0; $i < $iter; $i++)
{
$pow = (1 + (2 * $i));
$mul = bcdiv("1.0", $pow);
$fraction = bcmul($mul, bcpow(bcsub($a, "1.0") / bcadd($a, "1.0"), $pow));
$result = bcadd($fraction, $result);
}

return
bcmul("2.0", $result);
}

/*
* Computes the base2 log using baseN log.
* @note Requires above functions.
* @author Thomas Oldbury.
* @license Public domain.
*/
function bclog2($a, $iter = 10)
{
return
bcdiv(bcln($a, $iter), bcln("2", $iter));
}

/*
* Computes the base10 log using baseN log.
* @note Requires above functions.
* @author Thomas Oldbury.
* @license Public domain.
*/
function bclog10($a, $iter = 10)
{
return
bcdiv(bcln($a, $iter), bcln("10", $iter));
}


?>
up
-3
Anonymous
19 years ago
Well, if bcpow has limits, then this should work:
<?php
function bcpow_($num, $power) {
$awnser = "1";
while (
$power) {
$awnser = bcmul($awnser, $num, 100);
$power = bcsub($power, "1");
}
return
rtrim($awnser, '0.');
}
?>
Just that $power cannot have decimal digits in it.
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