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
16namespace angle
17{
18
19namespace base
20{
21
22// Convenience function that returns true if the supplied value is in range
23// for the destination type.
24template <typename Dst, typename Src>
25constexpr 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.
32template <typename T>
33constexpr 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
40template <typename T>
41constexpr 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.
50template <typename Dst, typename Src>
51inline 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).
58struct 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.
69struct SaturatedCastNaNBehaviorReturnZero
70{
71 template <typename T>
72 static constexpr T HandleNaN()
73 {
74 return T();
75 }
76};
77
78namespace 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.
82template <typename Dst, class NaNHandler, typename Src>
83constexpr 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.
101template <typename Dst, class NaNHandler = SaturatedCastNaNBehaviorReturnZero, typename Src>
102constexpr 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.
113template <typename Dst, typename Src>
114constexpr 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.
140template <typename T>
141class 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.
171typedef StrictNumeric<size_t> SizeT;
172
173} // namespace base
174
175} // namespace angle
176
177#endif // ANGLEBASE_NUMERICS_SAFE_CONVERSIONS_H_
178