1 | // Copyright 2014 The Chromium Authors. All rights reserved. |
2 | // Use of this source code is governed by a BSD-style license that can be |
3 | // found in the LICENSE file. |
4 | |
5 | #ifndef ANGLEBASE_NUMERICS_SAFE_CONVERSIONS_H_ |
6 | #define ANGLEBASE_NUMERICS_SAFE_CONVERSIONS_H_ |
7 | |
8 | #include <stddef.h> |
9 | |
10 | #include <limits> |
11 | #include <type_traits> |
12 | |
13 | #include "anglebase/logging.h" |
14 | #include "anglebase/numerics/safe_conversions_impl.h" |
15 | |
16 | namespace angle |
17 | { |
18 | |
19 | namespace base |
20 | { |
21 | |
22 | // Convenience function that returns true if the supplied value is in range |
23 | // for the destination type. |
24 | template <typename Dst, typename Src> |
25 | constexpr bool IsValueInRangeForNumericType(Src value) |
26 | { |
27 | return internal::DstRangeRelationToSrcRange<Dst>(value) == internal::RANGE_VALID; |
28 | } |
29 | |
30 | // Convenience function for determining if a numeric value is negative without |
31 | // throwing compiler warnings on: unsigned(value) < 0. |
32 | template <typename T> |
33 | constexpr typename std::enable_if<std::numeric_limits<T>::is_signed, bool>::type IsValueNegative( |
34 | T value) |
35 | { |
36 | static_assert(std::numeric_limits<T>::is_specialized, "Argument must be numeric." ); |
37 | return value < 0; |
38 | } |
39 | |
40 | template <typename T> |
41 | constexpr typename std::enable_if<!std::numeric_limits<T>::is_signed, bool>::type IsValueNegative(T) |
42 | { |
43 | static_assert(std::numeric_limits<T>::is_specialized, "Argument must be numeric." ); |
44 | return false; |
45 | } |
46 | |
47 | // checked_cast<> is analogous to static_cast<> for numeric types, |
48 | // except that it CHECKs that the specified numeric conversion will not |
49 | // overflow or underflow. NaN source will always trigger a CHECK. |
50 | template <typename Dst, typename Src> |
51 | inline Dst checked_cast(Src value) |
52 | { |
53 | CHECK(IsValueInRangeForNumericType<Dst>(value)); |
54 | return static_cast<Dst>(value); |
55 | } |
56 | |
57 | // HandleNaN will cause this class to CHECK(false). |
58 | struct SaturatedCastNaNBehaviorCheck |
59 | { |
60 | template <typename T> |
61 | static T HandleNaN() |
62 | { |
63 | CHECK(false); |
64 | return T(); |
65 | } |
66 | }; |
67 | |
68 | // HandleNaN will return 0 in this case. |
69 | struct SaturatedCastNaNBehaviorReturnZero |
70 | { |
71 | template <typename T> |
72 | static constexpr T HandleNaN() |
73 | { |
74 | return T(); |
75 | } |
76 | }; |
77 | |
78 | namespace internal |
79 | { |
80 | // This wrapper is used for C++11 constexpr support by avoiding the declaration |
81 | // of local variables in the saturated_cast template function. |
82 | template <typename Dst, class NaNHandler, typename Src> |
83 | constexpr Dst saturated_cast_impl(const Src value, const RangeConstraint constraint) |
84 | { |
85 | return constraint == RANGE_VALID |
86 | ? static_cast<Dst>(value) |
87 | : (constraint == RANGE_UNDERFLOW |
88 | ? std::numeric_limits<Dst>::min() |
89 | : (constraint == RANGE_OVERFLOW |
90 | ? std::numeric_limits<Dst>::max() |
91 | : (constraint == RANGE_INVALID |
92 | ? NaNHandler::template HandleNaN<Dst>() |
93 | : (NOTREACHED(), static_cast<Dst>(value))))); |
94 | } |
95 | } // namespace internal |
96 | |
97 | // saturated_cast<> is analogous to static_cast<> for numeric types, except |
98 | // that the specified numeric conversion will saturate rather than overflow or |
99 | // underflow. NaN assignment to an integral will defer the behavior to a |
100 | // specified class. By default, it will return 0. |
101 | template <typename Dst, class NaNHandler = SaturatedCastNaNBehaviorReturnZero, typename Src> |
102 | constexpr Dst saturated_cast(Src value) |
103 | { |
104 | return std::numeric_limits<Dst>::is_iec559 |
105 | ? static_cast<Dst>(value) // Floating point optimization. |
106 | : internal::saturated_cast_impl<Dst, NaNHandler>( |
107 | value, internal::DstRangeRelationToSrcRange<Dst>(value)); |
108 | } |
109 | |
110 | // strict_cast<> is analogous to static_cast<> for numeric types, except that |
111 | // it will cause a compile failure if the destination type is not large enough |
112 | // to contain any value in the source type. It performs no runtime checking. |
113 | template <typename Dst, typename Src> |
114 | constexpr Dst strict_cast(Src value) |
115 | { |
116 | static_assert(std::numeric_limits<Src>::is_specialized, "Argument must be numeric." ); |
117 | static_assert(std::numeric_limits<Dst>::is_specialized, "Result must be numeric." ); |
118 | static_assert((internal::StaticDstRangeRelationToSrcRange<Dst, Src>::value == |
119 | internal::NUMERIC_RANGE_CONTAINED), |
120 | "The numeric conversion is out of range for this type. You " |
121 | "should probably use one of the following conversion " |
122 | "mechanisms on the value you want to pass:\n" |
123 | "- base::checked_cast\n" |
124 | "- base::saturated_cast\n" |
125 | "- base::CheckedNumeric" ); |
126 | |
127 | return static_cast<Dst>(value); |
128 | } |
129 | |
130 | // StrictNumeric implements compile time range checking between numeric types by |
131 | // wrapping assignment operations in a strict_cast. This class is intended to be |
132 | // used for function arguments and return types, to ensure the destination type |
133 | // can always contain the source type. This is essentially the same as enforcing |
134 | // -Wconversion in gcc and C4302 warnings on MSVC, but it can be applied |
135 | // incrementally at API boundaries, making it easier to convert code so that it |
136 | // compiles cleanly with truncation warnings enabled. |
137 | // This template should introduce no runtime overhead, but it also provides no |
138 | // runtime checking of any of the associated mathematical operations. Use |
139 | // CheckedNumeric for runtime range checks of the actual value being assigned. |
140 | template <typename T> |
141 | class StrictNumeric |
142 | { |
143 | public: |
144 | typedef T type; |
145 | |
146 | constexpr StrictNumeric() : value_(0) {} |
147 | |
148 | // Copy constructor. |
149 | template <typename Src> |
150 | constexpr StrictNumeric(const StrictNumeric<Src> &rhs) : value_(strict_cast<T>(rhs.value_)) |
151 | {} |
152 | |
153 | // This is not an explicit constructor because we implicitly upgrade regular |
154 | // numerics to StrictNumerics to make them easier to use. |
155 | template <typename Src> |
156 | constexpr StrictNumeric(Src value) : value_(strict_cast<T>(value)) |
157 | {} |
158 | |
159 | // The numeric cast operator basically handles all the magic. |
160 | template <typename Dst> |
161 | constexpr operator Dst() const |
162 | { |
163 | return strict_cast<Dst>(value_); |
164 | } |
165 | |
166 | private: |
167 | const T value_; |
168 | }; |
169 | |
170 | // Explicitly make a shorter size_t typedef for convenience. |
171 | typedef StrictNumeric<size_t> SizeT; |
172 | |
173 | } // namespace base |
174 | |
175 | } // namespace angle |
176 | |
177 | #endif // ANGLEBASE_NUMERICS_SAFE_CONVERSIONS_H_ |
178 | |