bcpow
(PHP 4, PHP 5)
bcpow — Raise an arbitrary precision number to another
Description
string bcpow
( string
$left_operand
, string $right_operand
[, int $scale
] )
Raise left_operand to the power
right_operand.
Parameters
-
left_operand -
The left operand, as a string.
-
right_operand -
The right operand, as a string.
-
scale -
This optional parameter is used to set the number of digits after the decimal place in the result. You can also set the global default scale for all functions by using bcscale().
Return Values
Returns the result as a string.
Examples
Example #1 bcpow() example
<?php
echo bcpow('4.2', '3', 2); // 74.08
?>
Notes
Note:
bcpow() may return a result with fewer digits after the decimal point than the
scaleparameter would indicate. This only occurs when the result doesn't require all of the precision allowed by thescale. For example:Example #2 bcpow() scale example
<?php
echo bcpow('5', '2', 2); // prints "25", not "25.00"
?>
See Also
- bcpowmod() - Raise an arbitrary precision number to another, reduced by a specified modulus
- bcsqrt() - Get the square root of an arbitrary precision number
Коментарии
bcpow() only supports exponents less than or equal to 2^31-1. Also, bcpow() does not support decimal numbers. If you have scale set to 0, then the exponent is converted to an interger; otherwise an error is generated.
--
Michael Bailey
http://www.jinxidoru.com
Well, if bcpow has limits, then this should work:<?php
function bcpow_($num, $power) {
$awnser = "1";
while ($power) {
$awnser = bcmul($awnser, $num, 100);
$power = bcsub($power, "1");
}
return rtrim($awnser, '0.');
}
?>
Just that $power cannot have decimal digits in it.
<?php
bcscale(100);
/*
* Computes the natural logarithm using a series.
* @author Thomas Oldbury.
* @license Public domain.
*/
function bcln($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));
}
?>