RosettaCodeData/Task/Modular-exponentiation/D/modular-exponentiation.d

module modular_exponentiation;

private import std.bigint;

BigInt powMod(BigInt base, BigInt exponent, in BigInt modulus)
pure nothrow /*@safe*/ in {
   assert(exponent >= 0);
} body {
    BigInt result = 1;

    while (exponent) {
        if (exponent & 1)
            result = (result * base) % modulus;
        exponent /= 2;
        base = base ^^ 2 % modulus;
    }

    return result;
}

version (modular_exponentiation)
    void main() {
        import std.stdio;

        powMod(BigInt("29883481620585741369158914214988194" ~
                      "66320163312926952423791023078876139"),
               BigInt("235139930337346448646612254452369009" ~
                      "4744975233415544072992656881240319"),
               BigInt(10) ^^ 40).writeln;
    }