bcpow

(PHP 4, PHP 5, PHP 7)

bcpow — 任意精度数字的乘方

说明

string bcpow ( string $left_operand , string $right_operand [, int $scale ] )

左操作数的右操作数次方运算.

参数

left_operand

字符串类型的左操作数.

right_operand

字符串类型的右操作数.

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。

返回值

返回结果为字符串类型.

范例

Example #1 bcpow() 示例

<?php

echo bcpow('4.2', '3', 2); // 74.08

?>

注释

Note:

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 09:19
<?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 10:58
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) 10-Aug-2004 02:42
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