/*

 * (C) Copyright Projet SECRET, INRIA, Rocquencourt

 * (C) Bhaskar Biswas and  Nicolas Sendrier

 *

 * (C) 2014 cryptosource GmbH

 * (C) 2014 Falko Strenzke fstrenzke@cryptosource.de

 *

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

 *

 */

#ifndef BOTAN_POLYN_GF2M_H_

#define BOTAN_POLYN_GF2M_H_

#include <botan/secmem.h>

#include <utility>

#include <string>

namespace Botan {

typedef uint16_t gf2m;

class GF2m_Field;

class RandomNumberGenerator;

class polyn_gf2m

   {

   public:

      /**

      * create a zero polynomial:

      */

      explicit polyn_gf2m(const std::shared_ptr<GF2m_Field>& sp_field);

      polyn_gf2m() : m_deg(-1) {}

      polyn_gf2m(const secure_vector<uint8_t>& encoded,

                 const std::shared_ptr<GF2m_Field>& sp_field);

      polyn_gf2m& operator=(const polyn_gf2m&) = default;

      /**

      * create zero polynomial with reservation of space for a degree d polynomial

      */

      polyn_gf2m(int d, const std::shared_ptr<GF2m_Field>& sp_field);

      polyn_gf2m(polyn_gf2m const& other);

      /**

      * random irreducible polynomial of degree t

      */

      polyn_gf2m(size_t t, RandomNumberGenerator& rng,

                 const std::shared_ptr<GF2m_Field>& sp_field);

      /** decode a polynomial from memory: **/

      polyn_gf2m(const uint8_t* mem, uint32_t mem_len, const std::shared_ptr<GF2m_Field>& sp_field);

      /**

      *  create a polynomial from memory area (encoded)

      */

      polyn_gf2m(int degree, const uint8_t* mem, size_t mem_byte_len,

                 const std::shared_ptr<GF2m_Field>& sp_field);

      bool operator==(const polyn_gf2m & other) const ;

      bool operator!=(const polyn_gf2m & other) const { return !(*this == other); }

      polyn_gf2m(polyn_gf2m&& other)

         {

         this->swap(other);

         }

      polyn_gf2m & operator=(polyn_gf2m&& other)

         {

         if(this != &other)

            {

            this->swap(other);

            }

         return *this;

         }

      void swap(polyn_gf2m& other);

      secure_vector<uint8_t> encode() const;

      std::shared_ptr<GF2m_Field> get_sp_field() const

         { return m_sp_field; }

      gf2m& operator[](size_t i) { return m_coeff[i]; }

      gf2m operator[](size_t i) const { return m_coeff[i]; }

      gf2m get_lead_coef() const { return m_coeff[m_deg]; }

      gf2m get_coef(size_t i) const { return m_coeff[i]; }

      inline void set_coef(size_t i, gf2m v)

         {

         m_coeff[i] = v;

         }

      inline void add_to_coef(size_t i, gf2m v)

         {

         m_coeff[i] ^= v;

         }

      std::string to_string() const;

      void encode(uint32_t min_numo_coeffs, uint8_t* mem, uint32_t mem_len) const;

      int get_degree() const;

      /**

      * determine the degree in a timing secure manner. the timing of this function

      * only depends on the number of allocated coefficients, not on the actual

      * degree

      */

      int calc_degree_secure() const;

      size_t degppf(const polyn_gf2m& g);

      static std::vector<polyn_gf2m> sqmod_init(const polyn_gf2m & g);

      static std::vector<polyn_gf2m> sqrt_mod_init(const polyn_gf2m & g);

      polyn_gf2m sqmod(const std::vector<polyn_gf2m> & sq, int d);

      void set_to_zero();

      gf2m eval(gf2m a);

      static std::pair<polyn_gf2m, polyn_gf2m> eea_with_coefficients(const polyn_gf2m & p,

                                                                     const polyn_gf2m & g,

                                                                     int break_deg);

      void patchup_deg_secure( uint32_t trgt_deg, gf2m patch_elem);

   private:

      void set_degree(int d) { m_deg = d; }

      void poly_shiftmod( const polyn_gf2m & g);

      void realloc(uint32_t new_size);

      static polyn_gf2m gcd(polyn_gf2m const& p1, polyn_gf2m const& p2);

      /**

      * destructive:

      */

      static void remainder(polyn_gf2m & p, const polyn_gf2m & g);

      static polyn_gf2m gcd_aux(polyn_gf2m& p1, polyn_gf2m& p2);

   private:

      int m_deg;

      secure_vector<gf2m> m_coeff;

      std::shared_ptr<GF2m_Field> m_sp_field;

   };

gf2m random_gf2m(RandomNumberGenerator& rng);

gf2m random_code_element(uint16_t code_length, RandomNumberGenerator& rng);

std::vector<polyn_gf2m> syndrome_init(polyn_gf2m const& generator, std::vector<gf2m> const& support, int n);

/**

* Find the roots of a polynomial over GF(2^m) using the method by Federenko et al.

*/

secure_vector<gf2m> find_roots_gf2m_decomp(const polyn_gf2m & polyn, size_t code_length);

}

#endif