/*************************************************
* GMP Modular Exponentiation Source File         *
* (C) 1999-2007 Jack Lloyd                       *
*************************************************/

#include <botan/eng_gmp.h>
#include <botan/gmp_wrap.h>

namespace Botan {

namespace {

/*************************************************
* GMP Modular Exponentiator                      *
*************************************************/
class GMP_Modular_Exponentiator : public Modular_Exponentiator
   {
   public:
      void set_base(const BigInt& b) { base = b; }
      void set_exponent(const BigInt& e) { exp = e; }
      BigInt execute() const;
      Modular_Exponentiator* copy() const
         { return new GMP_Modular_Exponentiator(*this); }

      GMP_Modular_Exponentiator(const BigInt& n) : mod(n) {}
   private:
      GMP_MPZ base, exp, mod;
   };

/*************************************************
* Compute the result                             *
*************************************************/
BigInt GMP_Modular_Exponentiator::execute() const
   {
   GMP_MPZ r;
   mpz_powm(r.value, base.value, exp.value, mod.value);
   return r.to_bigint();
   }

}

/*************************************************
* Return the GMP-based modular exponentiator     *
*************************************************/
Modular_Exponentiator* GMP_Engine::mod_exp(const BigInt& n,
                                           Power_Mod::Usage_Hints) const
   {
   return new GMP_Modular_Exponentiator(n);
   }

}