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
|
/**
* Copyright (C) 2016 MongoDB Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the GNU Affero General Public License in all respects
* for all of the code used other than as permitted herein. If you modify
* file(s) with this exception, you may extend this exception to your
* version of the file(s), but you are not obligated to do so. If you do not
* wish to do so, delete this exception statement from your version. If you
* delete this exception statement from all source files in the program,
* then also delete it in the license file.
*/
#pragma once
#include <cmath>
#include <limits>
#include <type_traits>
#include <boost/optional.hpp>
#include "mongo/base/static_assert.h"
#include "mongo/stdx/type_traits.h"
namespace mongo {
namespace detail {
/**
* The following three methods are conversion helpers that allow us to promote
* all numerical input to three top-level types: int64_t, uint64_t, and double.
*/
// Floating point numbers -> double
template <typename T>
typename stdx::enable_if_t<std::is_floating_point<T>::value, double> upconvert(T t) {
MONGO_STATIC_ASSERT(sizeof(double) >= sizeof(T));
return static_cast<double>(t);
}
// Signed integral types -> int64_t
template <typename T>
typename stdx::enable_if_t<std::is_integral<T>::value && std::is_signed<T>::value, int64_t>
upconvert(T t) {
MONGO_STATIC_ASSERT(sizeof(int64_t) >= sizeof(T));
return static_cast<int64_t>(t);
}
// Unsigned integral types -> uint64_t
template <typename T>
typename stdx::enable_if_t<std::is_integral<T>::value && !std::is_signed<T>::value, uint64_t>
upconvert(T t) {
MONGO_STATIC_ASSERT(sizeof(uint64_t) >= sizeof(T));
return static_cast<uint64_t>(t);
}
/**
* Compare two values of the same type. Return -1 if a < b, 0 if they are equal, and
* 1 if a > b.
*/
template <typename T>
int identityCompare(T a, T b) {
if (a == b) {
return 0;
}
return (a < b) ? -1 : 1;
}
inline int signedCompare(int64_t a, int64_t b) {
return identityCompare(a, b);
}
inline int signedCompare(double a, double b) {
return identityCompare(a, b);
}
inline int signedCompare(uint64_t a, uint64_t b) {
return identityCompare(a, b);
}
/**
* Compare unsigned and signed integers.
*/
inline int signedCompare(int64_t a, uint64_t b) {
if (a < 0) {
return -1;
}
auto aUnsigned = static_cast<uint64_t>(a);
return signedCompare(aUnsigned, b);
}
inline int signedCompare(uint64_t a, int64_t b) {
return -signedCompare(b, a);
}
/**
* Compare doubles and signed integers.
*/
inline int signedCompare(double a, int64_t b) {
// Casting int64_ts to doubles will round them
// and give the wrong result, so convert doubles to
// int64_ts if we can, then do the comparison.
if (a < -std::ldexp(1, 63)) {
return -1;
} else if (a >= std::ldexp(1, 63)) {
return 1;
}
auto aAsInt64 = static_cast<int64_t>(a);
return signedCompare(aAsInt64, b);
}
inline int signedCompare(int64_t a, double b) {
return -signedCompare(b, a);
}
/**
* Compare doubles and unsigned integers.
*/
inline int signedCompare(double a, uint64_t b) {
if (a < 0) {
return -1;
}
// Casting uint64_ts to doubles will round them
// and give the wrong result, so convert doubles to
// uint64_ts if we can, then do the comparison.
if (a >= std::ldexp(1, 64)) {
return 1;
}
auto aAsUInt64 = static_cast<uint64_t>(a);
return signedCompare(aAsUInt64, b);
}
inline int signedCompare(uint64_t a, double b) {
return -signedCompare(b, a);
}
/**
* For any t and u of types T and U, promote t and u to one of the
* top-level numerical types (int64_t, uint64_t, and double) and
* compare them.
*
* Return -1 if t < u, 0 if they are equal, 1 if t > u.
*/
template <typename T, typename U>
int compare(T t, U u) {
return signedCompare(upconvert(t), upconvert(u));
}
} // namespace detail
/**
* Given a number of some type Input and a desired numerical type Output,
* this method represents the input number in the output type if possible.
* If the given number cannot be exactly represented in the output type,
* this method returns a disengaged optional.
*
* ex:
* auto v1 = representAs<int>(2147483647); // v1 holds 2147483647
* auto v2 = representAs<int>(2147483648); // v2 is disengaged
* auto v3 = representAs<int>(10.3); // v3 is disengaged
*/
template <typename Output, typename Input>
boost::optional<Output> representAs(Input number) {
if (std::is_same<Input, Output>::value) {
return {static_cast<Output>(number)};
}
// If number is NaN and Output can also represent NaN, return NaN
// Note: We need to specifically handle NaN here because of the way
// detail::compare is implemented.
{
// We use ADL here to allow types, such as Decimal, to supply their
// own definitions of isnan(). If the Input type does not define a
// custom isnan(), then we fall back to using std::isnan().
using std::isnan;
if (std::is_floating_point<Input>::value && isnan(number)) {
if (std::is_floating_point<Output>::value) {
return {static_cast<Output>(number)};
}
}
}
// If Output is integral and number is a non-integral floating point value,
// return a disengaged optional.
if (std::is_floating_point<Input>::value && std::is_integral<Output>::value) {
if (!(std::trunc(number) == number)) {
return {};
}
}
const auto floor = std::numeric_limits<Output>::lowest();
const auto ceiling = std::numeric_limits<Output>::max();
// If number is out-of-bounds for Output type, fail.
if ((detail::compare(number, floor) < 0) || (detail::compare(number, ceiling) > 0)) {
return {};
}
// Our number is within bounds, safe to perform a static_cast.
auto numberOut = static_cast<Output>(number);
// Some integers cannot be exactly represented as floating point numbers.
// To check, we cast back to the input type if we can, and compare.
if (std::is_integral<Input>::value && std::is_floating_point<Output>::value) {
const auto inputFloor = std::numeric_limits<Input>::lowest();
const auto inputCeiling = std::numeric_limits<Input>::max();
// If it is not safe to cast back to the Input type, fail.
if ((detail::compare(numberOut, inputFloor) < 0) ||
(detail::compare(numberOut, inputCeiling) > 0)) {
return {};
}
if (number != static_cast<Input>(numberOut)) {
return {};
}
}
return {static_cast<Output>(numberOut)};
}
} // namespace mongo
|
