PHP bcpowmod function

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bcpowmod

(PHP 5)

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.

Note:
Because this method uses the modulus operation, non-natural numbers
may give unexpected results. A natural number is any positive
non-zero integer.

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.