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 $scale = null): string
num 的 exponent 次方运算。
参数
-
num -
string 类型的底数。
-
exponent -
string 类型的指数。 如果指数不是整数，将被截断。 指数的有效范围取决于平台，但起码支持
-2147483648到2147483647的范围。 -
scale -
此可选参数用于设置结果中小数点后的小数位数。也可通过使用 bcscale() 来设置全局默认的小数位数，用于所有函数。如果未设置，则默认为
0。
返回值
返回字符串类型的结果。
更新日志
| 版本 | 说明 |
|---|---|
| 7.3.0 | 现在 bcpow() 可以按想要的小数点位数返回数字。 而之前，返回的数字会忽略尾随零（trailing decimal zeroes）。 |
范例
示例 #1 bcpow() 示例
<?php
echo bcpow('4.2', '3', 2); // 74.08
?>
注释
注意:
Before PHP 7.3.0 bcpow() may return a result with fewer digits after the decimal point than the
scaleparameter would indicate. This only occurs when the result doesn't require all of the precision allowed by thescale. For example:示例 #2 bcpow() scale example
<?php
echo bcpow('5', '2', 2); // prints "25", not "25.00"
?>
参见
- bcpowmod() - Raise an arbitrary precision number to another, reduced by a specified modulus
- bcsqrt() - 任意精度数字的二次方根
add a note
User Contributed Notes 3 notes
thomas at tgohome dot com ¶
12 years ago
<?php
bcscale(100);
/*
* Computes the natural logarithm using a series.
* @author Thomas Oldbury.
* @license Public domain.
*/
function bcln($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", $iter));
}
?>
Anonymous ¶
17 years ago
Well, if bcpow has limits, then this should work:
<?php
function bcpow_($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.
Michael Bailey (jinxidoru at byu dot net) ¶
17 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