PHP Manual: BcMath\Number::powmod

Description

public function BcMath\Number::powmod(BcMath\Number|string|int $exponent, BcMath\Number|string|int $modulus, ?int $scale = null): BcMath\Number

Use the fast-exponentiation method to raise $this to the power exponent with respect to the modulus modulus.

Parameters

exponent: The exponent, as an non-negative and integral (i.e. the scale has to be zero).
modulus: The modulus, as an integral (i.e. the scale has to be zero).
scale: BcMath\Number::scale explicitly specified for calculation results. If null, the BcMath\Number::scale of the calculation result will be set automatically.

Return Values

Returns the result as a new BcMath\Number object.

When the BcMath\Number::scale of the result object is automatically set, the BcMath\Number::scale of the result object will always be 0.

Errors/Exceptions

This method throws a ValueError in the following cases:

exponent or modulus is string and not a well-formed BCMath numeric string
$this, exponent or modulus has a fractional part
exponent is a negative value
scale is outside the valid range

This method throws a DivisionByZeroError exception if modulus is 0.

Examples

Example #1 BcMath\Number::powmod() example when scale is not specified

<?php
var_dump(
    new BcMath\Number('8')->powmod(new BcMath\Number('3'), 5),
    new BcMath\Number('-8')->powmod(new BcMath\Number('3'), 5),
    new BcMath\Number('8')->powmod('2', -3),
    new BcMath\Number('-8')->powmod(5, 7),
);
?>

The above example will output:

object(BcMath\Number)#3 (2) {
  ["value"]=>
  string(1) "2"
  ["scale"]=>
  int(0)
}
object(BcMath\Number)#4 (2) {
  ["value"]=>
  string(2) "-2"
  ["scale"]=>
  int(0)
}
object(BcMath\Number)#2 (2) {
  ["value"]=>
  string(1) "1"
  ["scale"]=>
  int(0)
}
object(BcMath\Number)#5 (2) {
  ["value"]=>
  string(2) "-1"
  ["scale"]=>
  int(0)
}

Example #2 BcMath\Number::powmod() example of explicitly specifying scale

<?php
var_dump(
    new BcMath\Number('8')->powmod(new BcMath\Number('3'), 5, 1),
    new BcMath\Number('-8')->powmod(new BcMath\Number('3'), 5, 2),
    new BcMath\Number('8')->powmod('2', -3, 3),
    new BcMath\Number('-8')->powmod(5, 7, 4),
);
?>