libstdc++
uniform_int_dist.h
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1// Class template uniform_int_distribution -*- C++ -*-
2
3// Copyright (C) 2009-2016 Free Software Foundation, Inc.
4//
5// This file is part of the GNU ISO C++ Library. This library is free
6// software; you can redistribute it and/or modify it under the
7// terms of the GNU General Public License as published by the
8// Free Software Foundation; either version 3, or (at your option)
9// any later version.
10
11// This library is distributed in the hope that it will be useful,
12// but WITHOUT ANY WARRANTY; without even the implied warranty of
13// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14// GNU General Public License for more details.
15
16// Under Section 7 of GPL version 3, you are granted additional
17// permissions described in the GCC Runtime Library Exception, version
18// 3.1, as published by the Free Software Foundation.
19
20// You should have received a copy of the GNU General Public License and
21// a copy of the GCC Runtime Library Exception along with this program;
22// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23// <http://www.gnu.org/licenses/>.
24
25/**
26 * @file bits/uniform_int_dist.h
27 * This is an internal header file, included by other library headers.
28 * Do not attempt to use it directly. @headername{random}
29 */
30
31#ifndef _GLIBCXX_BITS_UNIFORM_INT_DIST_H
32#define _GLIBCXX_BITS_UNIFORM_INT_DIST_H
33
34#include <type_traits>
35#include <limits>
36
37namespace std _GLIBCXX_VISIBILITY(default)
38{
39
40 namespace __detail
41 {
42_GLIBCXX_BEGIN_NAMESPACE_VERSION
43 /* Determine whether number is a power of 2. */
44 template<typename _Tp>
45 inline bool
46 _Power_of_2(_Tp __x)
47 {
48 return ((__x - 1) & __x) == 0;
49 };
50_GLIBCXX_END_NAMESPACE_VERSION
51 }
52
53_GLIBCXX_BEGIN_NAMESPACE_VERSION
54
55 /**
56 * @brief Uniform discrete distribution for random numbers.
57 * A discrete random distribution on the range @f$[min, max]@f$ with equal
58 * probability throughout the range.
59 */
60 template<typename _IntType = int>
62 {
64 "template argument not an integral type");
65
66 public:
67 /** The type of the range of the distribution. */
68 typedef _IntType result_type;
69 /** Parameter type. */
71 {
73
74 explicit
75 param_type(_IntType __a = 0,
77 : _M_a(__a), _M_b(__b)
78 {
79 __glibcxx_assert(_M_a <= _M_b);
80 }
81
83 a() const
84 { return _M_a; }
85
87 b() const
88 { return _M_b; }
89
90 friend bool
91 operator==(const param_type& __p1, const param_type& __p2)
92 { return __p1._M_a == __p2._M_a && __p1._M_b == __p2._M_b; }
93
94 private:
95 _IntType _M_a;
96 _IntType _M_b;
97 };
98
99 public:
100 /**
101 * @brief Constructs a uniform distribution object.
102 */
103 explicit
104 uniform_int_distribution(_IntType __a = 0,
105 _IntType __b = std::numeric_limits<_IntType>::max())
106 : _M_param(__a, __b)
107 { }
108
109 explicit
110 uniform_int_distribution(const param_type& __p)
111 : _M_param(__p)
112 { }
113
114 /**
115 * @brief Resets the distribution state.
116 *
117 * Does nothing for the uniform integer distribution.
118 */
119 void
120 reset() { }
121
123 a() const
124 { return _M_param.a(); }
125
127 b() const
128 { return _M_param.b(); }
129
130 /**
131 * @brief Returns the parameter set of the distribution.
132 */
133 param_type
134 param() const
135 { return _M_param; }
136
137 /**
138 * @brief Sets the parameter set of the distribution.
139 * @param __param The new parameter set of the distribution.
140 */
141 void
143 { _M_param = __param; }
144
145 /**
146 * @brief Returns the inclusive lower bound of the distribution range.
147 */
149 min() const
150 { return this->a(); }
151
152 /**
153 * @brief Returns the inclusive upper bound of the distribution range.
154 */
156 max() const
157 { return this->b(); }
158
159 /**
160 * @brief Generating functions.
161 */
162 template<typename _UniformRandomNumberGenerator>
165 { return this->operator()(__urng, _M_param); }
166
167 template<typename _UniformRandomNumberGenerator>
170 const param_type& __p);
171
172 template<typename _ForwardIterator,
174 void
175 __generate(_ForwardIterator __f, _ForwardIterator __t,
177 { this->__generate(__f, __t, __urng, _M_param); }
178
179 template<typename _ForwardIterator,
180 typename _UniformRandomNumberGenerator>
181 void
182 __generate(_ForwardIterator __f, _ForwardIterator __t,
183 _UniformRandomNumberGenerator& __urng,
184 const param_type& __p)
185 { this->__generate_impl(__f, __t, __urng, __p); }
186
187 template<typename _UniformRandomNumberGenerator>
188 void
189 __generate(result_type* __f, result_type* __t,
190 _UniformRandomNumberGenerator& __urng,
191 const param_type& __p)
192 { this->__generate_impl(__f, __t, __urng, __p); }
193
194 /**
195 * @brief Return true if two uniform integer distributions have
196 * the same parameters.
197 */
198 friend bool
201 { return __d1._M_param == __d2._M_param; }
202
203 private:
204 template<typename _ForwardIterator,
206 void
207 __generate_impl(_ForwardIterator __f, _ForwardIterator __t,
209 const param_type& __p);
210
211 param_type _M_param;
212 };
213
214 template<typename _IntType>
215 template<typename _UniformRandomNumberGenerator>
218 operator()(_UniformRandomNumberGenerator& __urng,
219 const param_type& __param)
220 {
221 typedef typename _UniformRandomNumberGenerator::result_type
222 _Gresult_type;
223 typedef typename std::make_unsigned<result_type>::type __utype;
225 __uctype;
226
227 const __uctype __urngmin = __urng.min();
228 const __uctype __urngmax = __urng.max();
229 const __uctype __urngrange = __urngmax - __urngmin;
230 const __uctype __urange
231 = __uctype(__param.b()) - __uctype(__param.a());
232
233 __uctype __ret;
234
235 if (__urngrange > __urange)
236 {
237 // downscaling
238 const __uctype __uerange = __urange + 1; // __urange can be zero
239 const __uctype __scaling = __urngrange / __uerange;
240 const __uctype __past = __uerange * __scaling;
241 do
242 __ret = __uctype(__urng()) - __urngmin;
243 while (__ret >= __past);
244 __ret /= __scaling;
245 }
246 else if (__urngrange < __urange)
247 {
248 // upscaling
249 /*
250 Note that every value in [0, urange]
251 can be written uniquely as
252
253 (urngrange + 1) * high + low
254
255 where
256
257 high in [0, urange / (urngrange + 1)]
258
259 and
260
261 low in [0, urngrange].
262 */
263 __uctype __tmp; // wraparound control
264 do
265 {
266 const __uctype __uerngrange = __urngrange + 1;
267 __tmp = (__uerngrange * operator()
268 (__urng, param_type(0, __urange / __uerngrange)));
269 __ret = __tmp + (__uctype(__urng()) - __urngmin);
270 }
271 while (__ret > __urange || __ret < __tmp);
272 }
273 else
274 __ret = __uctype(__urng()) - __urngmin;
275
276 return __ret + __param.a();
277 }
278
279
280 template<typename _IntType>
281 template<typename _ForwardIterator,
282 typename _UniformRandomNumberGenerator>
283 void
284 uniform_int_distribution<_IntType>::
285 __generate_impl(_ForwardIterator __f, _ForwardIterator __t,
286 _UniformRandomNumberGenerator& __urng,
287 const param_type& __param)
288 {
289 __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
290 typedef typename _UniformRandomNumberGenerator::result_type
291 _Gresult_type;
292 typedef typename std::make_unsigned<result_type>::type __utype;
294 __uctype;
295
296 const __uctype __urngmin = __urng.min();
297 const __uctype __urngmax = __urng.max();
298 const __uctype __urngrange = __urngmax - __urngmin;
299 const __uctype __urange
300 = __uctype(__param.b()) - __uctype(__param.a());
301
302 __uctype __ret;
303
304 if (__urngrange > __urange)
305 {
306 if (__detail::_Power_of_2(__urngrange + 1)
307 && __detail::_Power_of_2(__urange + 1))
308 {
309 while (__f != __t)
310 {
311 __ret = __uctype(__urng()) - __urngmin;
312 *__f++ = (__ret & __urange) + __param.a();
313 }
314 }
315 else
316 {
317 // downscaling
318 const __uctype __uerange = __urange + 1; // __urange can be zero
319 const __uctype __scaling = __urngrange / __uerange;
320 const __uctype __past = __uerange * __scaling;
321 while (__f != __t)
322 {
323 do
324 __ret = __uctype(__urng()) - __urngmin;
325 while (__ret >= __past);
326 *__f++ = __ret / __scaling + __param.a();
327 }
328 }
329 }
330 else if (__urngrange < __urange)
331 {
332 // upscaling
333 /*
334 Note that every value in [0, urange]
335 can be written uniquely as
336
337 (urngrange + 1) * high + low
338
339 where
340
341 high in [0, urange / (urngrange + 1)]
342
343 and
344
345 low in [0, urngrange].
346 */
347 __uctype __tmp; // wraparound control
348 while (__f != __t)
349 {
350 do
351 {
352 const __uctype __uerngrange = __urngrange + 1;
353 __tmp = (__uerngrange * operator()
354 (__urng, param_type(0, __urange / __uerngrange)));
355 __ret = __tmp + (__uctype(__urng()) - __urngmin);
356 }
357 while (__ret > __urange || __ret < __tmp);
358 *__f++ = __ret;
359 }
360 }
361 else
362 while (__f != __t)
363 *__f++ = __uctype(__urng()) - __urngmin + __param.a();
364 }
365
366_GLIBCXX_END_NAMESPACE_VERSION
367} // namespace std
368
369#endif
ISO C++ entities toplevel namespace is std.
Properties of fundamental types.
Definition limits:316
is_integral
Definition type_traits:324
Uniform discrete distribution for random numbers. A discrete random distribution on the range with e...
void reset()
Resets the distribution state.
result_type operator()(_UniformRandomNumberGenerator &__urng)
Generating functions.
void param(const param_type &__param)
Sets the parameter set of the distribution.
result_type min() const
Returns the inclusive lower bound of the distribution range.
friend bool operator==(const uniform_int_distribution &__d1, const uniform_int_distribution &__d2)
Return true if two uniform integer distributions have the same parameters.
uniform_int_distribution(_IntType __a=0, _IntType __b=std::numeric_limits< _IntType >::max())
Constructs a uniform distribution object.
result_type max() const
Returns the inclusive upper bound of the distribution range.
param_type param() const
Returns the parameter set of the distribution.