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1 /* | 1 /* |
2 * Copyright 2016 The WebRTC Project Authors. All rights reserved. | 2 * Copyright 2016 The WebRTC Project Authors. All rights reserved. |
3 * | 3 * |
4 * Use of this source code is governed by a BSD-style license | 4 * Use of this source code is governed by a BSD-style license |
5 * that can be found in the LICENSE file in the root of the source | 5 * that can be found in the LICENSE file in the root of the source |
6 * tree. An additional intellectual property rights grant can be found | 6 * tree. An additional intellectual property rights grant can be found |
7 * in the file PATENTS. All contributing project authors may | 7 * in the file PATENTS. All contributing project authors may |
8 * be found in the AUTHORS file in the root of the source tree. | 8 * be found in the AUTHORS file in the root of the source tree. |
9 */ | 9 */ |
10 | 10 |
11 // This file defines six constexpr functions: | 11 // This file defines six constexpr functions: |
12 // | 12 // |
13 // rtc::safe_cmp::Eq // == | 13 // rtc::SafeEq // == |
14 // rtc::safe_cmp::Ne // != | 14 // rtc::SafeNe // != |
15 // rtc::safe_cmp::Lt // < | 15 // rtc::SafeLt // < |
16 // rtc::safe_cmp::Le // <= | 16 // rtc::SafeLe // <= |
17 // rtc::safe_cmp::Gt // > | 17 // rtc::SafeGt // > |
18 // rtc::safe_cmp::Ge // >= | 18 // rtc::SafeGe // >= |
19 // | 19 // |
20 // They each accept two arguments of arbitrary types, and in almost all cases, | 20 // They each accept two arguments of arbitrary types, and in almost all cases, |
21 // they simply call the appropriate comparison operator. However, if both | 21 // they simply call the appropriate comparison operator. However, if both |
22 // arguments are integers, they don't compare them using C++'s quirky rules, | 22 // arguments are integers, they don't compare them using C++'s quirky rules, |
23 // but instead adhere to the true mathematical definitions. It is as if the | 23 // but instead adhere to the true mathematical definitions. It is as if the |
24 // arguments were first converted to infinite-range signed integers, and then | 24 // arguments were first converted to infinite-range signed integers, and then |
25 // compared, although of course nothing expensive like that actually takes | 25 // compared, although of course nothing expensive like that actually takes |
26 // place. In practice, for signed/signed and unsigned/unsigned comparisons and | 26 // place. In practice, for signed/signed and unsigned/unsigned comparisons and |
27 // some mixed-signed comparisons with a compile-time constant, the overhead is | 27 // some mixed-signed comparisons with a compile-time constant, the overhead is |
28 // zero; in the remaining cases, it is just a few machine instructions (no | 28 // zero; in the remaining cases, it is just a few machine instructions (no |
29 // branches). | 29 // branches). |
30 | 30 |
31 #ifndef WEBRTC_BASE_SAFE_COMPARE_H_ | 31 #ifndef WEBRTC_BASE_SAFE_COMPARE_H_ |
32 #define WEBRTC_BASE_SAFE_COMPARE_H_ | 32 #define WEBRTC_BASE_SAFE_COMPARE_H_ |
33 | 33 |
34 #include <stddef.h> | 34 #include <stddef.h> |
35 #include <stdint.h> | 35 #include <stdint.h> |
36 | 36 |
37 #include <type_traits> | 37 #include <type_traits> |
38 #include <utility> | 38 #include <utility> |
39 | 39 |
40 #include "webrtc/base/type_traits.h" | 40 #include "webrtc/base/type_traits.h" |
41 | 41 |
42 namespace rtc { | 42 namespace rtc { |
43 namespace safe_cmp { | |
44 | 43 |
45 namespace safe_cmp_impl { | 44 namespace safe_cmp_impl { |
46 | 45 |
47 template <size_t N> | 46 template <size_t N> |
48 struct LargerIntImpl : std::false_type {}; | 47 struct LargerIntImpl : std::false_type {}; |
49 template <> | 48 template <> |
50 struct LargerIntImpl<sizeof(int8_t)> : std::true_type { | 49 struct LargerIntImpl<sizeof(int8_t)> : std::true_type { |
51 using type = int16_t; | 50 using type = int16_t; |
52 }; | 51 }; |
53 template <> | 52 template <> |
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146 RTC_SAFECMP_MAKE_OP(GtOp, >) | 145 RTC_SAFECMP_MAKE_OP(GtOp, >) |
147 RTC_SAFECMP_MAKE_OP(GeOp, >=) | 146 RTC_SAFECMP_MAKE_OP(GeOp, >=) |
148 #undef RTC_SAFECMP_MAKE_OP | 147 #undef RTC_SAFECMP_MAKE_OP |
149 | 148 |
150 } // namespace safe_cmp_impl | 149 } // namespace safe_cmp_impl |
151 | 150 |
152 #define RTC_SAFECMP_MAKE_FUN(name) \ | 151 #define RTC_SAFECMP_MAKE_FUN(name) \ |
153 template <typename T1, typename T2> \ | 152 template <typename T1, typename T2> \ |
154 constexpr \ | 153 constexpr \ |
155 typename std::enable_if<IsIntlike<T1>::value && IsIntlike<T2>::value, \ | 154 typename std::enable_if<IsIntlike<T1>::value && IsIntlike<T2>::value, \ |
156 bool>::type \ | 155 bool>::type Safe##name(T1 a, T2 b) { \ |
157 name(T1 a, T2 b) { \ | |
158 /* Unary plus here turns enums into real integral types. */ \ | 156 /* Unary plus here turns enums into real integral types. */ \ |
159 return safe_cmp_impl::Cmp<safe_cmp_impl::name##Op>(+a, +b); \ | 157 return safe_cmp_impl::Cmp<safe_cmp_impl::name##Op>(+a, +b); \ |
160 } \ | 158 } \ |
161 template <typename T1, typename T2> \ | 159 template <typename T1, typename T2> \ |
162 constexpr \ | 160 constexpr \ |
163 typename std::enable_if<!IsIntlike<T1>::value || !IsIntlike<T2>::value, \ | 161 typename std::enable_if<!IsIntlike<T1>::value || !IsIntlike<T2>::value, \ |
164 bool>::type \ | 162 bool>::type Safe##name(const T1& a, \ |
165 name(const T1& a, const T2& b) { \ | 163 const T2& b) { \ |
166 return safe_cmp_impl::name##Op::Op(a, b); \ | 164 return safe_cmp_impl::name##Op::Op(a, b); \ |
167 } | 165 } |
168 RTC_SAFECMP_MAKE_FUN(Eq) | 166 RTC_SAFECMP_MAKE_FUN(Eq) |
169 RTC_SAFECMP_MAKE_FUN(Ne) | 167 RTC_SAFECMP_MAKE_FUN(Ne) |
170 RTC_SAFECMP_MAKE_FUN(Lt) | 168 RTC_SAFECMP_MAKE_FUN(Lt) |
171 RTC_SAFECMP_MAKE_FUN(Le) | 169 RTC_SAFECMP_MAKE_FUN(Le) |
172 RTC_SAFECMP_MAKE_FUN(Gt) | 170 RTC_SAFECMP_MAKE_FUN(Gt) |
173 RTC_SAFECMP_MAKE_FUN(Ge) | 171 RTC_SAFECMP_MAKE_FUN(Ge) |
174 #undef RTC_SAFECMP_MAKE_FUN | 172 #undef RTC_SAFECMP_MAKE_FUN |
175 | 173 |
176 } // namespace safe_cmp | |
177 } // namespace rtc | 174 } // namespace rtc |
178 | 175 |
179 #endif // WEBRTC_BASE_SAFE_COMPARE_H_ | 176 #endif // WEBRTC_BASE_SAFE_COMPARE_H_ |
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