PHP中文手册_PHP教程_PHP实例:Raise an arbitrary precision number to another, reduced by a specified modulus

bcpowmod(
    string $num,
    string $exponent,
    string $modulus,
    ?int $scale = null
): string

Use the fast-exponentiation method to raise num to the power exponent with respect to the modulus modulus.

num: The base, as an integral string (i.e. the scale has to be zero).
exponent: The exponent, as an non-negative, integral string (i.e. the scale has to be zero).
modulus: The modulus, as an integral string (i.e. the scale has to be zero).
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。

Returns the result as a string, or false if modulus is 0 or exponent is negative.

版本	说明
8.0.0	`scale` is now nullable.

The following two statements are functionally identical. The bcpowmod() version however, executes in less time and can accept larger parameters.


<?php
$a = bcpowmod($x, $y, $mod);

$b = bcmod(bcpow($x, $y), $mod);

// $a and $b are equal to each other.

?>

注意:
Because this method uses the modulus operation, numbers which are not positive integers may give unexpected results.