(PHP 5, PHP 7)
bcpowmod — Raise an arbitrary precision number to another, reduced by a specified modulus
$scale= 0 ] ) : string
Use the fast-exponentiation method to raise
base to the power
exponent with respect to the modulus
The base, as an integral string (i.e. the scale has to be zero).
The exponent, as an non-negative, integral string (i.e. the scale has to be zero).
The modulus, as an integral string (i.e. the scale has to be zero).
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。
Returns the result as a string, or
is 0 or
exponent is negative.
Because this method uses the modulus operation, numbers which are not positive integers may give unexpected results.
The following two statements are functionally identical. The bcpowmod() version however, executes in less time and can accept larger parameters.
$a = bcpowmod($x, $y, $mod);
$b = bcmod(bcpow($x, $y), $mod);
// $a and $b are equal to each other.