/* boost random/uniform_smallint.hpp header file

 *

 * Copyright Jens Maurer 2000-2001

 * 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: uniform_smallint.hpp 41369 2007-11-25 18:07:19Z bemandawes $

 *

 * Revision history

 *  2001-04-08  added min<max assertion (N. Becker)

 *  2001-02-18  moved to individual header files

 */



#ifndef BOOST_RANDOM_UNIFORM_SMALLINT_HPP

#define BOOST_RANDOM_UNIFORM_SMALLINT_HPP



#include <cassert>

#include <iostream>

#include <boost/config.hpp>

#include <boost/limits.hpp>

#include <boost/static_assert.hpp>

#include <boost/random/uniform_01.hpp>

#include <boost/detail/workaround.hpp>

#ifdef BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS

#include <boost/type_traits/is_float.hpp>

#endif





namespace boost {



// uniform integer distribution on a small range [min, max]



namespace detail {



template <class InputStream, class UniformInt, class Impl>

InputStream& extract_uniform_int(InputStream& is, UniformInt& ud, Impl& impl)

{

    typename UniformInt::result_type min, max;

    is >> std::ws >> min >> std::ws >> max;

    impl.set(min, max);

    return is;

}



template<class UniformRandomNumberGenerator, class IntType>

struct uniform_smallint_integer

{

public:

  typedef UniformRandomNumberGenerator base_type;

  typedef IntType result_type;



  uniform_smallint_integer(base_type & rng, IntType min_arg, IntType max_arg)

    : _rng(&rng)

  { set(min_arg, max_arg); }



  void set(result_type min, result_type max);

  

  result_type min BOOST_PREVENT_MACRO_SUBSTITUTION () const { return _min; }

  result_type max BOOST_PREVENT_MACRO_SUBSTITUTION () const { return _max; }

  base_type& base() const { return *_rng; }

  

  result_type operator()()

  {

    // we must not use the low bits here, because LCGs get very bad then

    return (((*_rng)() - (_rng->min)()) / _factor) % _range + _min;

  }



private:

  typedef typename base_type::result_type base_result;

  base_type * _rng;

  IntType _min, _max;

  base_result _range;

  base_result _factor;

};



template<class UniformRandomNumberGenerator, class IntType>

void uniform_smallint_integer<UniformRandomNumberGenerator, IntType>::

set(result_type min_arg, result_type max_arg) 

{

  _min = min_arg;

  _max = max_arg;

  assert(min_arg < max_arg);



  _range = static_cast<base_result>(_max-_min)+1;

  _factor = 1;

  

  // LCGs get bad when only taking the low bits.

  // (probably put this logic into a partial template specialization)

  // Check how many low bits we can ignore before we get too much

  // quantization error.

  base_result r_base = (_rng->max)() - (_rng->min)();

  if(r_base == (std::numeric_limits<base_result>::max)()) {

    _factor = 2;

    r_base /= 2;

  }

  r_base += 1;

  if(r_base % _range == 0) {

    // No quantization effects, good

    _factor = r_base / _range;

  } else {

    // carefully avoid overflow; pessimizing heree

    for( ; r_base/_range/32 >= _range; _factor *= 2)

      r_base /= 2;

  }

}



template<class UniformRandomNumberGenerator, class IntType>

class uniform_smallint_float

{

public:

  typedef UniformRandomNumberGenerator base_type;

  typedef IntType result_type;



  uniform_smallint_float(base_type & rng, IntType min_arg, IntType max_arg)

    : _rng(rng)

  {

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

#if !defined(BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS) && !(defined(BOOST_MSVC) && BOOST_MSVC <= 1300)

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

    BOOST_STATIC_ASSERT(!std::numeric_limits<typename base_type::result_type>::is_integer);

#endif



    assert(min_arg < max_arg);

    set(min_arg, max_arg);

  }



  void set(result_type min_arg, result_type max_arg)

  {

    _min = min_arg;

    _max = max_arg;

    _range = static_cast<base_result>(_max-_min)+1;

  }



  result_type min BOOST_PREVENT_MACRO_SUBSTITUTION () const { return _min; }

  result_type max BOOST_PREVENT_MACRO_SUBSTITUTION () const { return _max; }

  base_type& base() const { return _rng.base(); }



  result_type operator()()

  {

    return static_cast<IntType>(_rng() * _range) + _min;

  }



private:

  typedef typename base_type::result_type base_result;

  uniform_01<base_type> _rng;

  IntType _min, _max;

  base_result _range;

};





} // namespace detail









template<class IntType = int>

class uniform_smallint

{

public:

  typedef IntType input_type;

  typedef IntType result_type;



  explicit uniform_smallint(IntType min_arg = 0, IntType max_arg = 9)

    : _min(min_arg), _max(max_arg)

  {

#ifndef BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS

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

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

#endif

 }



  result_type min BOOST_PREVENT_MACRO_SUBSTITUTION () const { return _min; }

  result_type max BOOST_PREVENT_MACRO_SUBSTITUTION () const { return _max; }

  void reset() { }



  template<class Engine>

  result_type operator()(Engine& eng)

  {

    typedef typename Engine::result_type base_result;

    base_result _range = static_cast<base_result>(_max-_min)+1;

    base_result _factor = 1;

    

    // LCGs get bad when only taking the low bits.

    // (probably put this logic into a partial template specialization)

    // Check how many low bits we can ignore before we get too much

    // quantization error.

    base_result r_base = (eng.max)() - (eng.min)();

    if(r_base == (std::numeric_limits<base_result>::max)()) {

      _factor = 2;

      r_base /= 2;

    }

    r_base += 1;

    if(r_base % _range == 0) {

      // No quantization effects, good

      _factor = r_base / _range;

    } else {

      // carefully avoid overflow; pessimizing heree

      for( ; r_base/_range/32 >= _range; _factor *= 2)

        r_base /= 2;

    }



    return ((eng() - (eng.min)()) / _factor) % _range + _min;

  }



#if !defined(BOOST_NO_OPERATORS_IN_NAMESPACE) && !defined(BOOST_NO_MEMBER_TEMPLATE_FRIENDS)

  template<class CharT, class Traits>

  friend std::basic_ostream<CharT,Traits>&

  operator<<(std::basic_ostream<CharT,Traits>& os, const uniform_smallint& ud)

  {

    os << ud._min << " " << ud._max;

    return os;

  }



  template<class CharT, class Traits>

  friend std::basic_istream<CharT,Traits>&

  operator>>(std::basic_istream<CharT,Traits>& is, uniform_smallint& ud)

  {

# if BOOST_WORKAROUND(_MSC_FULL_VER, BOOST_TESTED_AT(13102292)) && BOOST_MSVC > 1300

      return detail::extract_uniform_int(is, ud, ud._impl);

# else

    is >> std::ws >> ud._min >> std::ws >> ud._max;

    return is;

# endif

  }

#endif



private:

  result_type _min;

  result_type _max;

};



} // namespace boost



#endif // BOOST_RANDOM_UNIFORM_SMALLINT_HPP

