mfbt/IntegerTypeTraits.h@97036ab72558
mfbt/IntegerTypeTraits.h
Tue, 06 Jan 2015 21:39:09 +0100
- author
- Michael Schloh von Bennewitz <michael@schloh.com>
- date
- Tue, 06 Jan 2015 21:39:09 +0100
- branch
- TOR_BUG_9701
- changeset 8
- 97036ab72558
- permissions
- -rw-r--r--
Conditionally force memory storage according to privacy.thirdparty.isolate;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.
1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
3 /* This Source Code Form is subject to the terms of the Mozilla Public
4 * License, v. 2.0. If a copy of the MPL was not distributed with this
5 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
7 /* Helpers to manipulate integer types that don't fit in TypeTraits.h */
9 #ifndef mozilla_IntegerTypeTraits_h
10 #define mozilla_IntegerTypeTraits_h
12 #include "mozilla/TypeTraits.h"
13 #include <stdint.h>
15 namespace mozilla {
17 namespace detail {
19 /**
20 * StdintTypeForSizeAndSignedness returns the stdint integer type
21 * of given size (can be 1, 2, 4 or 8) and given signedness
22 * (false means unsigned, true means signed).
23 */
24 template<size_t Size, bool Signedness>
25 struct StdintTypeForSizeAndSignedness;
27 template<>
28 struct StdintTypeForSizeAndSignedness<1, true>
29 { typedef int8_t Type; };
31 template<>
32 struct StdintTypeForSizeAndSignedness<1, false>
33 { typedef uint8_t Type; };
35 template<>
36 struct StdintTypeForSizeAndSignedness<2, true>
37 { typedef int16_t Type; };
39 template<>
40 struct StdintTypeForSizeAndSignedness<2, false>
41 { typedef uint16_t Type; };
43 template<>
44 struct StdintTypeForSizeAndSignedness<4, true>
45 { typedef int32_t Type; };
47 template<>
48 struct StdintTypeForSizeAndSignedness<4, false>
49 { typedef uint32_t Type; };
51 template<>
52 struct StdintTypeForSizeAndSignedness<8, true>
53 { typedef int64_t Type; };
55 template<>
56 struct StdintTypeForSizeAndSignedness<8, false>
57 { typedef uint64_t Type; };
59 } // namespace detail
61 template<size_t Size>
62 struct UnsignedStdintTypeForSize
63 : detail::StdintTypeForSizeAndSignedness<Size, false>
64 {};
66 template<typename IntegerType>
67 struct PositionOfSignBit
68 {
69 static_assert(IsIntegral<IntegerType>::value, "PositionOfSignBit is only for integral types");
70 // 8 here should be CHAR_BIT from limits.h, but the world has moved on.
71 static const size_t value = 8 * sizeof(IntegerType) - 1;
72 };
74 /**
75 * MinValue returns the minimum value of the given integer type as a
76 * compile-time constant, which std::numeric_limits<IntegerType>::min()
77 * cannot do in c++98.
78 */
79 template<typename IntegerType>
80 struct MinValue
81 {
82 private:
83 static_assert(IsIntegral<IntegerType>::value, "MinValue is only for integral types");
85 typedef typename MakeUnsigned<IntegerType>::Type UnsignedIntegerType;
86 static const size_t PosOfSignBit = PositionOfSignBit<IntegerType>::value;
88 public:
89 // Bitwise ops may return a larger type, that's why we cast explicitly.
90 // In C++, left bit shifts on signed values is undefined by the standard
91 // unless the shifted value is representable.
92 // Notice that signed-to-unsigned conversions are always well-defined in
93 // the standard as the value congruent to 2**n, as expected. By contrast,
94 // unsigned-to-signed is only well-defined if the value is representable.
95 static const IntegerType value =
96 IsSigned<IntegerType>::value
97 ? IntegerType(UnsignedIntegerType(1) << PosOfSignBit)
98 : IntegerType(0);
99 };
101 /**
102 * MaxValue returns the maximum value of the given integer type as a
103 * compile-time constant, which std::numeric_limits<IntegerType>::max()
104 * cannot do in c++98.
105 */
106 template<typename IntegerType>
107 struct MaxValue
108 {
109 static_assert(IsIntegral<IntegerType>::value, "MaxValue is only for integral types");
111 // Tricksy, but covered by the CheckedInt unit test.
112 // Relies on the type of MinValue<IntegerType>::value
113 // being IntegerType.
114 static const IntegerType value = ~MinValue<IntegerType>::value;
115 };
117 } // namespace mozilla
119 #endif // mozilla_IntegerTypeTraits_h
