/* boost random/tausworthe.hpp header file

 *

 * Copyright Jens Maurer 2002

 * Distributed under the Boost Software License, Version 1.0. (See

 * accompanying file LICENSE_1_0.txt or copy at

 * http://www.boost.org/LICENSE_1_0.txt)

 *

 * See http://www.boost.org for most recent version including documentation.

 *

 * $Id: linear_feedback_shift.hpp 29116 2005-05-21 15:57:01Z dgregor $

 *

 */



#ifndef BOOST_RANDOM_LINEAR_FEEDBACK_SHIFT_HPP

#define BOOST_RANDOM_LINEAR_FEEDBACK_SHIFT_HPP



#include <iostream>

#include <cassert>

#include <stdexcept>

#include <boost/config.hpp>

#include <boost/static_assert.hpp>

#include <boost/limits.hpp>



namespace boost {

namespace random {



// Tausworte 1965

template<class UIntType, int w, int k, int q, int s, UIntType val>

class linear_feedback_shift

{

public:

  typedef UIntType result_type;

  // avoid the warning trouble when using (1<<w) on 32 bit machines

  BOOST_STATIC_CONSTANT(bool, has_fixed_range = false);

  BOOST_STATIC_CONSTANT(int, word_size = w);

  BOOST_STATIC_CONSTANT(int, exponent1 = k);

  BOOST_STATIC_CONSTANT(int, exponent2 = q);

  BOOST_STATIC_CONSTANT(int, step_size = s);



  result_type min BOOST_PREVENT_MACRO_SUBSTITUTION () const { return 0; }

  result_type max BOOST_PREVENT_MACRO_SUBSTITUTION () const { return wordmask; }



  // MSVC 6 and possibly others crash when encountering complicated integral

  // constant expressions.  Avoid the checks for now.

  // BOOST_STATIC_ASSERT(w > 0);

  // BOOST_STATIC_ASSERT(q > 0);

  // BOOST_STATIC_ASSERT(k < w);

  // BOOST_STATIC_ASSERT(0 < 2*q && 2*q < k);

  // BOOST_STATIC_ASSERT(0 < s && s <= k-q);



  explicit linear_feedback_shift(UIntType s0 = 341) : wordmask(0)

  {

    // MSVC fails BOOST_STATIC_ASSERT with std::numeric_limits at class scope

#ifndef BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS

    BOOST_STATIC_ASSERT(std::numeric_limits<UIntType>::is_integer);

    BOOST_STATIC_ASSERT(!std::numeric_limits<UIntType>::is_signed);

#endif



    // avoid "left shift count >= with of type" warning

    for(int i = 0; i < w; ++i)

      wordmask |= (1u << i);

    seed(s0);

  }



  template<class It> linear_feedback_shift(It& first, It last) : wordmask(0)

  {

    // MSVC fails BOOST_STATIC_ASSERT with std::numeric_limits at class scope

#ifndef BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS

    BOOST_STATIC_ASSERT(std::numeric_limits<UIntType>::is_integer);

    BOOST_STATIC_ASSERT(!std::numeric_limits<UIntType>::is_signed);

#endif



    // avoid "left shift count >= with of type" warning

    for(int i = 0; i < w; ++i)

      wordmask |= (1u << i);

    seed(first, last);

  }



  void seed(UIntType s0 = 341) { assert(s0 >= (1 << (w-k))); value = s0; }

  template<class It> void seed(It& first, It last)

  {

    if(first == last)

      throw std::invalid_argument("linear_feedback_shift::seed");

    value = *first++;

    assert(value >= (1 << (w-k)));

  }



  result_type operator()()

  {

    const UIntType b = (((value << q) ^ value) & wordmask) >> (k-s);

    const UIntType mask = ( (~static_cast<UIntType>(0)) << (w-k) ) & wordmask;

    value = ((value & mask) << s) ^ b;

    return value;

  }

  bool validation(result_type x) const { return val == x; }



#ifndef BOOST_NO_OPERATORS_IN_NAMESPACE



#ifndef BOOST_NO_MEMBER_TEMPLATE_FRIENDS

  template<class CharT, class Traits>

  friend std::basic_ostream<CharT,Traits>&

  operator<<(std::basic_ostream<CharT,Traits>& os, linear_feedback_shift x)

  { os << x.value; return os; }



  template<class CharT, class Traits>

  friend std::basic_istream<CharT,Traits>&

  operator>>(std::basic_istream<CharT,Traits>& is, linear_feedback_shift& x)

  { is >> x.value; return is; }

#endif



  friend bool operator==(linear_feedback_shift x, linear_feedback_shift y)

  { return x.value == y.value; }

  friend bool operator!=(linear_feedback_shift x, linear_feedback_shift y)

  { return !(x == y); }

#else

  // Use a member function; Streamable concept not supported.

  bool operator==(linear_feedback_shift rhs) const

  { return value == rhs.value; }

  bool operator!=(linear_feedback_shift rhs) const

  { return !(*this == rhs); }

#endif



private:

  UIntType wordmask; // avoid "left shift count >= width of type" warnings

  UIntType value;

};



#ifndef BOOST_NO_INCLASS_MEMBER_INITIALIZATION

//  A definition is required even for integral static constants

template<class UIntType, int w, int k, int q, int s, UIntType val>

const bool linear_feedback_shift<UIntType, w, k, q, s, val>::has_fixed_range;

template<class UIntType, int w, int k, int q, int s, UIntType val>

const int linear_feedback_shift<UIntType, w, k, q, s, val>::word_size;

template<class UIntType, int w, int k, int q, int s, UIntType val>

const int linear_feedback_shift<UIntType, w, k, q, s, val>::exponent1;

template<class UIntType, int w, int k, int q, int s, UIntType val>

const int linear_feedback_shift<UIntType, w, k, q, s, val>::exponent2;

template<class UIntType, int w, int k, int q, int s, UIntType val>

const int linear_feedback_shift<UIntType, w, k, q, s, val>::step_size;

#endif



} // namespace random

} // namespace boost



#endif // BOOST_RANDOM_LINEAR_FEEDBACK_SHIFT_HPP

