bcpowmod — Raise an arbitrary precision number to another, reduced by a specified modulus
Use the fast-exponentiation method to raise left_operand to the power right_operand with respect to the modulus modulus.
The left operand, as a string.
The right operand, as a string.
The modulus, as a string.
This optional parameter is used to set the number of digits after the decimal place in the result. You can also set the global default scale for all functions by using bcscale().
Returns the result as a string, or NULL if modulus is 0.
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.