/*

* Modular Reducer

* (C) 1999-2010 Jack Lloyd

*

* Botan is released under the Simplified BSD License (see license.txt)

*/

#ifndef BOTAN_MODULAR_REDUCER_H_

#define BOTAN_MODULAR_REDUCER_H_

#include <botan/bigint.h>

BOTAN_FUTURE_INTERNAL_HEADER(reducer.h)

namespace Botan {

/**

* Modular Reducer (using Barrett's technique)

*/

class BOTAN_PUBLIC_API(2, 0) Modular_Reducer final {

   public:

      const BigInt& get_modulus() const { return m_modulus; }

      BigInt reduce(const BigInt& x) const;

      /**

      * Multiply mod p

      * @param x the first operand

      * @param y the second operand

      * @return (x * y) % p

      */

      BigInt multiply(const BigInt& x, const BigInt& y) const { return reduce(x * y); }

      /**

      * Multiply mod p

      * @return (x * y * z) % p

      */

      BigInt multiply(const BigInt& x, const BigInt& y, const BigInt& z) const { return multiply(x, multiply(y, z)); }

      /**

      * Square mod p

      * @param x the value to square

      * @return (x * x) % p

      */

      BigInt square(const BigInt& x) const;

      /**

      * Cube mod p

      * @param x the value to cube

      * @return (x * x * x) % p

      */

      BigInt cube(const BigInt& x) const { return multiply(x, this->square(x)); }

      /**

      * Low level reduction function. Mostly for internal use.

      * Sometimes useful for performance by reducing temporaries

      * Reduce x mod p and place the output in out.

      *

      * @warning X and out must not reference each other

      *

      * ws is a temporary workspace.

      */

      void reduce(BigInt& out, const BigInt& x, secure_vector<word>& ws) const;

      bool initialized() const { return (m_mod_words != 0); }

      BOTAN_DEPRECATED("Use for_public_modulus or for_secret_modulus") Modular_Reducer() { m_mod_words = 0; }

      /**

      * Accepts m == 0 and leaves the Modular_Reducer in an uninitialized state

      */

      BOTAN_DEPRECATED("Use for_public_modulus or for_secret_modulus") explicit Modular_Reducer(const BigInt& mod);

      /**

      * Requires that m > 0

      */

      static Modular_Reducer for_public_modulus(const BigInt& m);

      /**

      * Requires that m > 0

      */

      static Modular_Reducer for_secret_modulus(const BigInt& m);

   private:

      Modular_Reducer(const BigInt& m, BigInt mu, size_t mw) : m_modulus(m), m_mu(std::move(mu)), m_mod_words(mw) {}

      BigInt m_modulus, m_mu;

      size_t m_mod_words;

};

}  // namespace Botan

#endif