bcpowmod

(PHP 5, PHP 7, PHP 8)

bcpowmod — 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: 此参数用于设置结果中的小数位数。如果为 null，则使用 bcscale() 设置的默认小数位数，或者回退到 bcmath.scale INI 指令的值。

Returns the result as a string.

This function throws a ValueError in the following cases:

This function throws a DivisionByZeroError exception if modulus is 0.

版本	说明
8.0.0	`scale` is now nullable.
8.0.0	Now throws a ValueError instead of returning `false` if `exponent` is a negative value.
8.0.0	Dividing by `0` now throws a DivisionByZeroError exception instead of returning `false`.

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.

bcpow() - 任意精度数字的乘方
bcmod() - 任意精度数字取模
BcMath\Number::powmod() - Raises an arbitrary precision number, reduced by a specified modulus