| /* |
| * Copyright 2016 The WebRTC Project Authors. All rights reserved. |
| * |
| * Use of this source code is governed by a BSD-style license |
| * that can be found in the LICENSE file in the root of the source |
| * tree. An additional intellectual property rights grant can be found |
| * in the file PATENTS. All contributing project authors may |
| * be found in the AUTHORS file in the root of the source tree. |
| */ |
| |
| // This file defines six constexpr functions: |
| // |
| // rtc::safe_cmp::Eq // == |
| // rtc::safe_cmp::Ne // != |
| // rtc::safe_cmp::Lt // < |
| // rtc::safe_cmp::Le // <= |
| // rtc::safe_cmp::Gt // > |
| // rtc::safe_cmp::Ge // >= |
| // |
| // They each accept two arguments of arbitrary types, and in almost all cases, |
| // they simply call the appropriate comparison operator. However, if both |
| // arguments are integers, they don't compare them using C++'s quirky rules, |
| // but instead adhere to the true mathematical definitions. It is as if the |
| // arguments were first converted to infinite-range signed integers, and then |
| // compared, although of course nothing expensive like that actually takes |
| // place. In practice, for signed/signed and unsigned/unsigned comparisons and |
| // some mixed-signed comparisons with a compile-time constant, the overhead is |
| // zero; in the remaining cases, it is just a few machine instructions (no |
| // branches). |
| |
| #ifndef WEBRTC_BASE_SAFE_COMPARE_H_ |
| #define WEBRTC_BASE_SAFE_COMPARE_H_ |
| |
| #include <stddef.h> |
| #include <stdint.h> |
| |
| #include <type_traits> |
| #include <utility> |
| |
| #include "webrtc/base/type_traits.h" |
| |
| namespace rtc { |
| namespace safe_cmp { |
| |
| namespace safe_cmp_impl { |
| |
| template <size_t N> |
| struct LargerIntImpl : std::false_type {}; |
| template <> |
| struct LargerIntImpl<sizeof(int8_t)> : std::true_type { |
| using type = int16_t; |
| }; |
| template <> |
| struct LargerIntImpl<sizeof(int16_t)> : std::true_type { |
| using type = int32_t; |
| }; |
| template <> |
| struct LargerIntImpl<sizeof(int32_t)> : std::true_type { |
| using type = int64_t; |
| }; |
| |
| // LargerInt<T1, T2>::value is true iff there's a signed type that's larger |
| // than T1 (and no larger than the larger of T2 and int*, for performance |
| // reasons); and if there is such a type, LargerInt<T1, T2>::type is an alias |
| // for it. |
| template <typename T1, typename T2> |
| struct LargerInt |
| : LargerIntImpl<sizeof(T1) < sizeof(T2) || sizeof(T1) < sizeof(int*) |
| ? sizeof(T1) |
| : 0> {}; |
| |
| template <typename T> |
| constexpr typename std::make_unsigned<T>::type MakeUnsigned(T a) { |
| return static_cast<typename std::make_unsigned<T>::type>(a); |
| } |
| |
| // Overload for when both T1 and T2 have the same signedness. |
| template <typename Op, |
| typename T1, |
| typename T2, |
| typename std::enable_if<std::is_signed<T1>::value == |
| std::is_signed<T2>::value>::type* = nullptr> |
| constexpr bool Cmp(T1 a, T2 b) { |
| return Op::Op(a, b); |
| } |
| |
| // Overload for signed - unsigned comparison that can be promoted to a bigger |
| // signed type. |
| template <typename Op, |
| typename T1, |
| typename T2, |
| typename std::enable_if<std::is_signed<T1>::value && |
| std::is_unsigned<T2>::value && |
| LargerInt<T2, T1>::value>::type* = nullptr> |
| constexpr bool Cmp(T1 a, T2 b) { |
| return Op::Op(a, static_cast<typename LargerInt<T2, T1>::type>(b)); |
| } |
| |
| // Overload for unsigned - signed comparison that can be promoted to a bigger |
| // signed type. |
| template <typename Op, |
| typename T1, |
| typename T2, |
| typename std::enable_if<std::is_unsigned<T1>::value && |
| std::is_signed<T2>::value && |
| LargerInt<T1, T2>::value>::type* = nullptr> |
| constexpr bool Cmp(T1 a, T2 b) { |
| return Op::Op(static_cast<typename LargerInt<T1, T2>::type>(a), b); |
| } |
| |
| // Overload for signed - unsigned comparison that can't be promoted to a bigger |
| // signed type. |
| template <typename Op, |
| typename T1, |
| typename T2, |
| typename std::enable_if<std::is_signed<T1>::value && |
| std::is_unsigned<T2>::value && |
| !LargerInt<T2, T1>::value>::type* = nullptr> |
| constexpr bool Cmp(T1 a, T2 b) { |
| return a < 0 ? Op::Op(-1, 0) : Op::Op(safe_cmp_impl::MakeUnsigned(a), b); |
| } |
| |
| // Overload for unsigned - signed comparison that can't be promoted to a bigger |
| // signed type. |
| template <typename Op, |
| typename T1, |
| typename T2, |
| typename std::enable_if<std::is_unsigned<T1>::value && |
| std::is_signed<T2>::value && |
| !LargerInt<T1, T2>::value>::type* = nullptr> |
| constexpr bool Cmp(T1 a, T2 b) { |
| return b < 0 ? Op::Op(0, -1) : Op::Op(a, safe_cmp_impl::MakeUnsigned(b)); |
| } |
| |
| #define RTC_SAFECMP_MAKE_OP(name, op) \ |
| struct name { \ |
| template <typename T1, typename T2> \ |
| static constexpr bool Op(T1 a, T2 b) { \ |
| return a op b; \ |
| } \ |
| }; |
| RTC_SAFECMP_MAKE_OP(EqOp, ==) |
| RTC_SAFECMP_MAKE_OP(NeOp, !=) |
| RTC_SAFECMP_MAKE_OP(LtOp, <) |
| RTC_SAFECMP_MAKE_OP(LeOp, <=) |
| RTC_SAFECMP_MAKE_OP(GtOp, >) |
| RTC_SAFECMP_MAKE_OP(GeOp, >=) |
| #undef RTC_SAFECMP_MAKE_OP |
| |
| } // namespace safe_cmp_impl |
| |
| #define RTC_SAFECMP_MAKE_FUN(name) \ |
| template <typename T1, typename T2> \ |
| constexpr \ |
| typename std::enable_if<IsIntlike<T1>::value && IsIntlike<T2>::value, \ |
| bool>::type \ |
| name(T1 a, T2 b) { \ |
| /* Unary plus here turns enums into real integral types. */ \ |
| return safe_cmp_impl::Cmp<safe_cmp_impl::name##Op>(+a, +b); \ |
| } \ |
| template <typename T1, typename T2> \ |
| constexpr \ |
| typename std::enable_if<!IsIntlike<T1>::value || !IsIntlike<T2>::value, \ |
| bool>::type \ |
| name(const T1& a, const T2& b) { \ |
| return safe_cmp_impl::name##Op::Op(a, b); \ |
| } |
| RTC_SAFECMP_MAKE_FUN(Eq) |
| RTC_SAFECMP_MAKE_FUN(Ne) |
| RTC_SAFECMP_MAKE_FUN(Lt) |
| RTC_SAFECMP_MAKE_FUN(Le) |
| RTC_SAFECMP_MAKE_FUN(Gt) |
| RTC_SAFECMP_MAKE_FUN(Ge) |
| #undef RTC_SAFECMP_MAKE_FUN |
| |
| } // namespace safe_cmp |
| } // namespace rtc |
| |
| #endif // WEBRTC_BASE_SAFE_COMPARE_H_ |
