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: 此可選參數用於設定結果中小數點后的小數位數。也可通過使用 bcscale() 來設定全域性預設的小數位數，用於所有函式。如果未設定，則預設為 0。

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

版本	說明
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.