/*

* 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/numthry.h>

namespace Botan {

/**

* Modular Reducer (using Barrett's technique)

*/

class BOTAN_PUBLIC_API(2,0) Modular_Reducer

   {

   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); }

      /**

      * Square mod p

      * @param x the value to square

      * @return (x * x) % p

      */

      BigInt square(const BigInt& x) const

         { return reduce(Botan::square(x)); }

      /**

      * 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. ** 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); }

      Modular_Reducer() { m_mod_words = 0; }

      explicit Modular_Reducer(const BigInt& mod);

   private:

      BigInt m_modulus, m_mu;

      size_t m_mod_words;

   };

}

#endif