(PHP 5, PHP 7, PHP 8)
bcpowmod — Raise an arbitrary precision number to another, reduced by a specified modulus
Use the fast-exponentiation method to raise
num to the power
exponent with respect to the modulus
modulus.
numThe base, as an integral string (i.e. the scale has to be zero).
exponentThe exponent, as an non-negative, integral string (i.e. the scale has to be zero).
modulusThe modulus, as an integral string (i.e. the scale has to be zero).
scalenull, it will default to the default scale set with bcscale(),
or fallback to the value of the
bcmath.scale INI directive.
Returns the result as a string.
This function throws a ValueError in the following cases:
num, exponent or modulus is not a well-formed BCMath numeric stringnum, exponent or modulus has a fractional partexponent is a negative valuescale is outside the valid range
This function throws a DivisionByZeroError exception if modulus
is 0.
| Version | Description |
|---|---|
| 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.
?>Note:
Because this method uses the modulus operation, numbers which are not positive integers may give unexpected results.