summaryrefslogtreecommitdiff
path: root/absl/random/internal/uniform_helper.h
blob: e68b82ee5c47fa80ccabc89a4c5d6c0f5d27a5a7 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
// Copyright 2019 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
#ifndef ABSL_RANDOM_INTERNAL_UNIFORM_HELPER_H_
#define ABSL_RANDOM_INTERNAL_UNIFORM_HELPER_H_

#include <cmath>
#include <limits>
#include <type_traits>

#include "absl/base/config.h"
#include "absl/meta/type_traits.h"
#include "absl/random/internal/traits.h"

namespace absl {
ABSL_NAMESPACE_BEGIN

template <typename IntType>
class uniform_int_distribution;

template <typename RealType>
class uniform_real_distribution;

// Interval tag types which specify whether the interval is open or closed
// on either boundary.

namespace random_internal {
template <typename T>
struct TagTypeCompare {};

template <typename T>
constexpr bool operator==(TagTypeCompare<T>, TagTypeCompare<T>) {
  // Tags are mono-states. They always compare equal.
  return true;
}
template <typename T>
constexpr bool operator!=(TagTypeCompare<T>, TagTypeCompare<T>) {
  return false;
}

}  // namespace random_internal

struct IntervalClosedClosedTag
    : public random_internal::TagTypeCompare<IntervalClosedClosedTag> {};
struct IntervalClosedOpenTag
    : public random_internal::TagTypeCompare<IntervalClosedOpenTag> {};
struct IntervalOpenClosedTag
    : public random_internal::TagTypeCompare<IntervalOpenClosedTag> {};
struct IntervalOpenOpenTag
    : public random_internal::TagTypeCompare<IntervalOpenOpenTag> {};

namespace random_internal {

// In the absence of an explicitly provided return-type, the template
// "uniform_inferred_return_t<A, B>" is used to derive a suitable type, based on
// the data-types of the endpoint-arguments {A lo, B hi}.
//
// Given endpoints {A lo, B hi}, one of {A, B} will be chosen as the
// return-type, if one type can be implicitly converted into the other, in a
// lossless way. The template "is_widening_convertible" implements the
// compile-time logic for deciding if such a conversion is possible.
//
// If no such conversion between {A, B} exists, then the overload for
// absl::Uniform() will be discarded, and the call will be ill-formed.
// Return-type for absl::Uniform() when the return-type is inferred.
template <typename A, typename B>
using uniform_inferred_return_t =
    absl::enable_if_t<absl::disjunction<is_widening_convertible<A, B>,
                                        is_widening_convertible<B, A>>::value,
                      typename std::conditional<
                          is_widening_convertible<A, B>::value, B, A>::type>;

// The functions
//    uniform_lower_bound(tag, a, b)
// and
//    uniform_upper_bound(tag, a, b)
// are used as implementation-details for absl::Uniform().
//
// Conceptually,
//    [a, b] == [uniform_lower_bound(IntervalClosedClosed, a, b),
//               uniform_upper_bound(IntervalClosedClosed, a, b)]
//    (a, b) == [uniform_lower_bound(IntervalOpenOpen, a, b),
//               uniform_upper_bound(IntervalOpenOpen, a, b)]
//    [a, b) == [uniform_lower_bound(IntervalClosedOpen, a, b),
//               uniform_upper_bound(IntervalClosedOpen, a, b)]
//    (a, b] == [uniform_lower_bound(IntervalOpenClosed, a, b),
//               uniform_upper_bound(IntervalOpenClosed, a, b)]
//
template <typename IntType, typename Tag>
typename absl::enable_if_t<
    absl::conjunction<
        IsIntegral<IntType>,
        absl::disjunction<std::is_same<Tag, IntervalOpenClosedTag>,
                          std::is_same<Tag, IntervalOpenOpenTag>>>::value,
    IntType>
uniform_lower_bound(Tag, IntType a, IntType) {
  return a < (std::numeric_limits<IntType>::max)() ? (a + 1) : a;
}

template <typename FloatType, typename Tag>
typename absl::enable_if_t<
    absl::conjunction<
        std::is_floating_point<FloatType>,
        absl::disjunction<std::is_same<Tag, IntervalOpenClosedTag>,
                          std::is_same<Tag, IntervalOpenOpenTag>>>::value,
    FloatType>
uniform_lower_bound(Tag, FloatType a, FloatType b) {
  return std::nextafter(a, b);
}

template <typename NumType, typename Tag>
typename absl::enable_if_t<
    absl::disjunction<std::is_same<Tag, IntervalClosedClosedTag>,
                      std::is_same<Tag, IntervalClosedOpenTag>>::value,
    NumType>
uniform_lower_bound(Tag, NumType a, NumType) {
  return a;
}

template <typename IntType, typename Tag>
typename absl::enable_if_t<
    absl::conjunction<
        IsIntegral<IntType>,
        absl::disjunction<std::is_same<Tag, IntervalClosedOpenTag>,
                          std::is_same<Tag, IntervalOpenOpenTag>>>::value,
    IntType>
uniform_upper_bound(Tag, IntType, IntType b) {
  return b > (std::numeric_limits<IntType>::min)() ? (b - 1) : b;
}

template <typename FloatType, typename Tag>
typename absl::enable_if_t<
    absl::conjunction<
        std::is_floating_point<FloatType>,
        absl::disjunction<std::is_same<Tag, IntervalClosedOpenTag>,
                          std::is_same<Tag, IntervalOpenOpenTag>>>::value,
    FloatType>
uniform_upper_bound(Tag, FloatType, FloatType b) {
  return b;
}

template <typename IntType, typename Tag>
typename absl::enable_if_t<
    absl::conjunction<
        IsIntegral<IntType>,
        absl::disjunction<std::is_same<Tag, IntervalClosedClosedTag>,
                          std::is_same<Tag, IntervalOpenClosedTag>>>::value,
    IntType>
uniform_upper_bound(Tag, IntType, IntType b) {
  return b;
}

template <typename FloatType, typename Tag>
typename absl::enable_if_t<
    absl::conjunction<
        std::is_floating_point<FloatType>,
        absl::disjunction<std::is_same<Tag, IntervalClosedClosedTag>,
                          std::is_same<Tag, IntervalOpenClosedTag>>>::value,
    FloatType>
uniform_upper_bound(Tag, FloatType, FloatType b) {
  return std::nextafter(b, (std::numeric_limits<FloatType>::max)());
}

// Returns whether the bounds are valid for the underlying distribution.
// Inputs must have already been resolved via uniform_*_bound calls.
//
// The c++ standard constraints in [rand.dist.uni.int] are listed as:
//    requires: lo <= hi.
//
// In the uniform_int_distrubtion, {lo, hi} are closed, closed. Thus:
// [0, 0] is legal.
// [0, 0) is not legal, but [0, 1) is, which translates to [0, 0].
// (0, 1) is not legal, but (0, 2) is, which translates to [1, 1].
// (0, 0] is not legal, but (0, 1] is, which translates to [1, 1].
//
// The c++ standard constraints in [rand.dist.uni.real] are listed as:
//    requires: lo <= hi.
//    requires: (hi - lo) <= numeric_limits<T>::max()
//
// In the uniform_real_distribution, {lo, hi} are closed, open, Thus:
// [0, 0] is legal, which is [0, 0+epsilon).
// [0, 0) is legal.
// (0, 0) is not legal, but (0-epsilon, 0+epsilon) is.
// (0, 0] is not legal, but (0, 0+epsilon] is.
//
template <typename FloatType>
absl::enable_if_t<std::is_floating_point<FloatType>::value, bool>
is_uniform_range_valid(FloatType a, FloatType b) {
  return a <= b && std::isfinite(b - a);
}

template <typename IntType>
absl::enable_if_t<IsIntegral<IntType>::value, bool>
is_uniform_range_valid(IntType a, IntType b) {
  return a <= b;
}

// UniformDistribution selects either absl::uniform_int_distribution
// or absl::uniform_real_distribution depending on the NumType parameter.
template <typename NumType>
using UniformDistribution =
    typename std::conditional<IsIntegral<NumType>::value,
                              absl::uniform_int_distribution<NumType>,
                              absl::uniform_real_distribution<NumType>>::type;

// UniformDistributionWrapper is used as the underlying distribution type
// by the absl::Uniform template function. It selects the proper Abseil
// uniform distribution and provides constructor overloads that match the
// expected parameter order as well as adjusting distribtuion bounds based
// on the tag.
template <typename NumType>
struct UniformDistributionWrapper : public UniformDistribution<NumType> {
  template <typename TagType>
  explicit UniformDistributionWrapper(TagType, NumType lo, NumType hi)
      : UniformDistribution<NumType>(
            uniform_lower_bound<NumType>(TagType{}, lo, hi),
            uniform_upper_bound<NumType>(TagType{}, lo, hi)) {}

  explicit UniformDistributionWrapper(NumType lo, NumType hi)
      : UniformDistribution<NumType>(
            uniform_lower_bound<NumType>(IntervalClosedOpenTag(), lo, hi),
            uniform_upper_bound<NumType>(IntervalClosedOpenTag(), lo, hi)) {}

  explicit UniformDistributionWrapper()
      : UniformDistribution<NumType>(std::numeric_limits<NumType>::lowest(),
                                     (std::numeric_limits<NumType>::max)()) {}
};

}  // namespace random_internal
ABSL_NAMESPACE_END
}  // namespace absl

#endif  // ABSL_RANDOM_INTERNAL_UNIFORM_HELPER_H_