(PHP 4, PHP 5, PHP 7, PHP 8)
bcpow — Raise an arbitrary precision number to another
Raise num to the power
exponent.
numThe base, as a string.
exponent
The exponent, as a string. Must be a value with no fractional part.
The valid range of the exponent is platform specific, but is at least
-2147483648 to 2147483647.
scalenull, it will default to the default scale set with bcscale(),
or fallback to the value of the
bcmath.scale INI directive.
Returns the result as a string.
This function throws a ValueError in the following cases:
num or exponent is not a well-formed BCMath numeric stringexponent has a fractional partexponent or scale is outside the valid range
This function throws a DivisionByZeroError exception if num
is 0 and exponent is a negative value.
| Version | Description |
|---|---|
| 8.4.0 |
Negative powers of 0 previously returned 0, but now throw a DivisionByZeroError
exception.
|
| 8.0.0 |
When exponent has a fractional part, it now throws a ValueError
instead of truncating.
|
| 7.3.0 | bcpow() now returns numbers with the requested scale. Formerly, the returned numbers may have omitted trailing decimal zeroes. |
Example #1 bcpow() example
<?php
echo bcpow('4.2', '3', 2); // 74.08
?>Note:
Before PHP 7.3.0 bcpow() may return a result with fewer digits after the decimal point than the
scaleparameter would indicate. This only occurs when the result doesn't require all of the precision allowed by thescale. For example:Example #2 bcpow() scale example
<?php
echo bcpow('5', '2', 2); // prints "25", not "25.00"
?>
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<?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));
}
?>