source: NonGTP/Boost/boost/random/uniform_int.hpp @ 857

Revision 857, 5.1 KB checked in by igarcia, 19 years ago (diff)
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1/* boost random/uniform_int.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: uniform_int.hpp,v 1.27 2004/07/27 03:43:32 dgregor Exp $
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_INT_HPP
18#define BOOST_RANDOM_UNIFORM_INT_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/detail/workaround.hpp>
26#include <boost/random/uniform_smallint.hpp>
27#include <boost/random/detail/signed_unsigned_compare.hpp>
28#ifdef BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS
29#include <boost/type_traits/is_float.hpp>
30#endif
31
32namespace boost {
33
34// uniform integer distribution on [min, max]
35template<class IntType = int>
36class uniform_int
37{
38public:
39  typedef IntType input_type;
40  typedef IntType result_type;
41
42  explicit uniform_int(IntType min = 0, IntType max = 9)
43    : _min(min), _max(max)
44  {
45#ifndef BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS
46    // MSVC fails BOOST_STATIC_ASSERT with std::numeric_limits at class scope
47    BOOST_STATIC_ASSERT(std::numeric_limits<IntType>::is_integer);
48#endif
49    assert(min <= max);
50    init();
51  }
52
53  result_type min BOOST_PREVENT_MACRO_SUBSTITUTION () const { return _min; }
54  result_type max BOOST_PREVENT_MACRO_SUBSTITUTION () const { return _max; }
55  void reset() { }
56 
57  // can't have member function templates out-of-line due to MSVC bugs
58  template<class Engine>
59  result_type operator()(Engine& eng)
60  {
61    typedef typename Engine::result_type base_result;
62    base_result bmin = (eng.min)();
63    base_result brange = (eng.max)() - (eng.min)();
64
65    if(_range == 0) {
66      return _min;   
67    } else if(random::equal_signed_unsigned(brange, _range)) {
68      // this will probably never happen in real life
69      // basically nothing to do; just take care we don't overflow / underflow
70      return static_cast<result_type>(eng() - bmin) + _min;
71    } else if(random::lessthan_signed_unsigned(brange, _range)) {
72      // use rejection method to handle things like 0..3 --> 0..4
73      for(;;) {
74        // concatenate several invocations of the base RNG
75        // take extra care to avoid overflows
76        result_type limit;
77        if(_range == (std::numeric_limits<result_type>::max)()) {
78          limit = _range/(result_type(brange)+1);
79          if(_range % result_type(brange)+1 == result_type(brange))
80            ++limit;
81        } else {
82          limit = (_range+1)/(result_type(brange)+1);
83        }
84        // We consider "result" as expressed to base (brange+1):
85        // For every power of (brange+1), we determine a random factor
86        result_type result = result_type(0);
87        result_type mult = result_type(1);
88        while(mult <= limit) {
89          result += (eng() - bmin) * mult;
90          mult *= result_type(brange)+result_type(1);
91        }
92        if(mult == limit)
93          // _range+1 is an integer power of brange+1: no rejections required
94          return result;
95        // _range/mult < brange+1  -> no endless loop
96        result += uniform_int<result_type>(0, _range/mult)(eng) * mult;
97        if(result <= _range)
98          return result + _min;
99      }
100    } else {                   // brange > range
101      if(brange / _range > 4 /* quantization_cutoff */ ) {
102        // the new range is vastly smaller than the source range,
103        // so quantization effects are not relevant
104        return boost::uniform_smallint<result_type>(_min, _max)(eng);
105      } else {
106        // use rejection method to handle cases like 0..5 -> 0..4
107        for(;;) {
108          base_result result = eng() - bmin;
109          // result and range are non-negative, and result is possibly larger
110          // than range, so the cast is safe
111          if(result <= static_cast<base_result>(_range))
112            return result + _min;
113        }
114      }
115    }
116  }
117
118#if !defined(BOOST_NO_OPERATORS_IN_NAMESPACE) && !defined(BOOST_NO_MEMBER_TEMPLATE_FRIENDS)
119  template<class CharT, class Traits>
120  friend std::basic_ostream<CharT,Traits>&
121  operator<<(std::basic_ostream<CharT,Traits>& os, const uniform_int& ud)
122  {
123    os << ud._min << " " << ud._max;
124    return os;
125  }
126
127  template<class CharT, class Traits>
128  friend std::basic_istream<CharT,Traits>&
129  operator>>(std::basic_istream<CharT,Traits>& is, uniform_int& ud)
130  {
131# if BOOST_WORKAROUND(_MSC_FULL_VER, BOOST_TESTED_AT(13102292)) && BOOST_MSVC > 1300
132      return detail::extract_uniform_int(is, ud, ud.impl);
133# else
134   is >> std::ws >> ud._min >> std::ws >> ud._max;
135    ud.init();
136    return is;
137# endif
138  }
139#endif
140
141private:
142  void init()
143  {
144    _range = _max - _min;
145  }
146   
147  result_type _min, _max, _range;
148};
149
150} // namespace boost
151
152#endif // BOOST_RANDOM_UNIFORM_INT_HPP
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