boost/random/uniform_smallint.hpp

   1 /* boost random/uniform_smallint.hpp header file
   2  *
   3  * Copyright Jens Maurer 2000-2001
   4  * Distributed under the Boost Software License, Version 1.0. (See
   5  * accompanying file LICENSE_1_0.txt or copy at
   6  * http://www.boost.org/LICENSE_1_0.txt)
   7  *
   8  * See http://www.boost.org for most recent version including documentation.
   9  *
  10  * $Id$
  11  *
  12  * Revision history
  13  *  2001-04-08  added min<max assertion (N. Becker)
  14  *  2001-02-18  moved to individual header files
  15  */
  16
  17 #ifndef BOOST_RANDOM_UNIFORM_SMALLINT_HPP
  18 #define BOOST_RANDOM_UNIFORM_SMALLINT_HPP
  19
  20 #include <cassert>
  21 #include <iostream>
  22 #include <boost/config.hpp>
  23 #include <boost/limits.hpp>
  24 #include <boost/static_assert.hpp>
  25 #include <boost/random/detail/config.hpp>
  26 #include <boost/random/uniform_01.hpp>
  27 #include <boost/detail/workaround.hpp>
  28
  29 namespace boost {
  30
  31 // uniform integer distribution on a small range [min, max]
  32
  33 template<class IntType = int>
  34 class uniform_smallint
  35 {
  36 public:
  37   typedef IntType input_type;
  38   typedef IntType result_type;
  39
  40   explicit uniform_smallint(IntType min_arg = 0, IntType max_arg = 9)
  41     : _min(min_arg), _max(max_arg)
  42   {
  43 #ifndef BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS
  44     // MSVC fails BOOST_STATIC_ASSERT with std::numeric_limits at class scope
  45     BOOST_STATIC_ASSERT(std::numeric_limits<IntType>::is_integer);
  46 #endif
  47  }
  48
  49   result_type min BOOST_PREVENT_MACRO_SUBSTITUTION () const { return _min; }
  50   result_type max BOOST_PREVENT_MACRO_SUBSTITUTION () const { return _max; }
  51   void reset() { }
  52
  53   template<class Engine>
  54   result_type operator()(Engine& eng)
  55   {
  56     typedef typename Engine::result_type base_result;
  57     base_result _range = static_cast<base_result>(_max-_min)+1;
  58     base_result _factor = 1;
  59
  60     // LCGs get bad when only taking the low bits.
  61     // (probably put this logic into a partial template specialization)
  62     // Check how many low bits we can ignore before we get too much
  63     // quantization error.
  64     base_result r_base = (eng.max)() - (eng.min)();
  65     if(r_base == (std::numeric_limits<base_result>::max)()) {
  66       _factor = 2;
  67       r_base /= 2;
  68     }
  69     r_base += 1;
  70     if(r_base % _range == 0) {
  71       // No quantization effects, good
  72       _factor = r_base / _range;
  73     } else {
  74       // carefully avoid overflow; pessimizing here
  75       for( ; r_base/_range/32 >= _range; _factor *= 2)
  76         r_base /= 2;
  77     }
  78
  79     return ((eng() - (eng.min)()) / _factor) % _range + _min;
  80   }
  81
  82 #ifndef BOOST_RANDOM_NO_STREAM_OPERATORS
  83   template<class CharT, class Traits>
  84   friend std::basic_ostream<CharT,Traits>&
  85   operator<<(std::basic_ostream<CharT,Traits>& os, const uniform_smallint& ud)
  86   {
  87     os << ud._min << " " << ud._max;
  88     return os;
  89   }
  90
  91   template<class CharT, class Traits>
  92   friend std::basic_istream<CharT,Traits>&
  93   operator>>(std::basic_istream<CharT,Traits>& is, uniform_smallint& ud)
  94   {
  95     is >> std::ws >> ud._min >> std::ws >> ud._max;
  96     return is;
  97   }
  98 #endif
  99
 100 private:
 101
 102   result_type _min;
 103   result_type _max;
 104 };
 105
 106 } // namespace boost
 107
 108 #endif // BOOST_RANDOM_UNIFORM_SMALLINT_HPP