bcpow()

(PHP 4, PHP 5, PHP 7)

任意精度数字的乘方

说明

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

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

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$scaleparameter would indicate. This only occurs when the result doesn't require all of the precision allowed by the$scale. For example:

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

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.

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));
}
?>