bcpow

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

bcpow — 任意精度数字的乘方

说明

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

num 的 exponent 次方运算。

参数

num: string 类型的底数。
exponent: string 类型的指数。如果指数不是整数，将被截断。指数的有效范围取决于平台，但起码支持 -2147483648 到 2147483647 的范围。
scale: 此可选参数用于设置结果中小数点后的小数位数。也可通过使用 bcscale() 来设置全局默认的小数位数，用于所有函数。如果未设置，则默认为 0。

返回值

返回字符串类型的结果。

更新日志

版本	说明
7.3.0	现在 bcpow() 可以按想要的小数点位数返回数字。而之前，返回的数字会忽略尾随零（trailing decimal zeroes）。

范例

Example #1 bcpow() 示例


<?php

echo bcpow('4.2', '3', 2); // 74.08

?>

注释

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" ?>

参见

bcpowmod() - Raise an arbitrary precision number to another, reduced by a specified modulus
bcsqrt() - 任意精度数字的二次方根

User Contributed Notes

thomas at tgohome dot com 13-Jul-2009 12:19


<?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));


}








?>

11-Feb-2005 01:58


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.

Michael Bailey (jinxidoru at byu dot net) 09-Aug-2004 05:42


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