mfbt/IntegerTypeTraits.h@97036ab72558 (annotated)
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.
| michael@0 | 1 | /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */ |
| michael@0 | 2 | /* vim: set ts=8 sts=2 et sw=2 tw=80: */ |
| michael@0 | 3 | /* This Source Code Form is subject to the terms of the Mozilla Public |
| michael@0 | 4 | * License, v. 2.0. If a copy of the MPL was not distributed with this |
| michael@0 | 5 | * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ |
| michael@0 | 6 | |
| michael@0 | 7 | /* Helpers to manipulate integer types that don't fit in TypeTraits.h */ |
| michael@0 | 8 | |
| michael@0 | 9 | #ifndef mozilla_IntegerTypeTraits_h |
| michael@0 | 10 | #define mozilla_IntegerTypeTraits_h |
| michael@0 | 11 | |
| michael@0 | 12 | #include "mozilla/TypeTraits.h" |
| michael@0 | 13 | #include <stdint.h> |
| michael@0 | 14 | |
| michael@0 | 15 | namespace mozilla { |
| michael@0 | 16 | |
| michael@0 | 17 | namespace detail { |
| michael@0 | 18 | |
| michael@0 | 19 | /** |
| michael@0 | 20 | * StdintTypeForSizeAndSignedness returns the stdint integer type |
| michael@0 | 21 | * of given size (can be 1, 2, 4 or 8) and given signedness |
| michael@0 | 22 | * (false means unsigned, true means signed). |
| michael@0 | 23 | */ |
| michael@0 | 24 | template<size_t Size, bool Signedness> |
| michael@0 | 25 | struct StdintTypeForSizeAndSignedness; |
| michael@0 | 26 | |
| michael@0 | 27 | template<> |
| michael@0 | 28 | struct StdintTypeForSizeAndSignedness<1, true> |
| michael@0 | 29 | { typedef int8_t Type; }; |
| michael@0 | 30 | |
| michael@0 | 31 | template<> |
| michael@0 | 32 | struct StdintTypeForSizeAndSignedness<1, false> |
| michael@0 | 33 | { typedef uint8_t Type; }; |
| michael@0 | 34 | |
| michael@0 | 35 | template<> |
| michael@0 | 36 | struct StdintTypeForSizeAndSignedness<2, true> |
| michael@0 | 37 | { typedef int16_t Type; }; |
| michael@0 | 38 | |
| michael@0 | 39 | template<> |
| michael@0 | 40 | struct StdintTypeForSizeAndSignedness<2, false> |
| michael@0 | 41 | { typedef uint16_t Type; }; |
| michael@0 | 42 | |
| michael@0 | 43 | template<> |
| michael@0 | 44 | struct StdintTypeForSizeAndSignedness<4, true> |
| michael@0 | 45 | { typedef int32_t Type; }; |
| michael@0 | 46 | |
| michael@0 | 47 | template<> |
| michael@0 | 48 | struct StdintTypeForSizeAndSignedness<4, false> |
| michael@0 | 49 | { typedef uint32_t Type; }; |
| michael@0 | 50 | |
| michael@0 | 51 | template<> |
| michael@0 | 52 | struct StdintTypeForSizeAndSignedness<8, true> |
| michael@0 | 53 | { typedef int64_t Type; }; |
| michael@0 | 54 | |
| michael@0 | 55 | template<> |
| michael@0 | 56 | struct StdintTypeForSizeAndSignedness<8, false> |
| michael@0 | 57 | { typedef uint64_t Type; }; |
| michael@0 | 58 | |
| michael@0 | 59 | } // namespace detail |
| michael@0 | 60 | |
| michael@0 | 61 | template<size_t Size> |
| michael@0 | 62 | struct UnsignedStdintTypeForSize |
| michael@0 | 63 | : detail::StdintTypeForSizeAndSignedness<Size, false> |
| michael@0 | 64 | {}; |
| michael@0 | 65 | |
| michael@0 | 66 | template<typename IntegerType> |
| michael@0 | 67 | struct PositionOfSignBit |
| michael@0 | 68 | { |
| michael@0 | 69 | static_assert(IsIntegral<IntegerType>::value, "PositionOfSignBit is only for integral types"); |
| michael@0 | 70 | // 8 here should be CHAR_BIT from limits.h, but the world has moved on. |
| michael@0 | 71 | static const size_t value = 8 * sizeof(IntegerType) - 1; |
| michael@0 | 72 | }; |
| michael@0 | 73 | |
| michael@0 | 74 | /** |
| michael@0 | 75 | * MinValue returns the minimum value of the given integer type as a |
| michael@0 | 76 | * compile-time constant, which std::numeric_limits<IntegerType>::min() |
| michael@0 | 77 | * cannot do in c++98. |
| michael@0 | 78 | */ |
| michael@0 | 79 | template<typename IntegerType> |
| michael@0 | 80 | struct MinValue |
| michael@0 | 81 | { |
| michael@0 | 82 | private: |
| michael@0 | 83 | static_assert(IsIntegral<IntegerType>::value, "MinValue is only for integral types"); |
| michael@0 | 84 | |
| michael@0 | 85 | typedef typename MakeUnsigned<IntegerType>::Type UnsignedIntegerType; |
| michael@0 | 86 | static const size_t PosOfSignBit = PositionOfSignBit<IntegerType>::value; |
| michael@0 | 87 | |
| michael@0 | 88 | public: |
| michael@0 | 89 | // Bitwise ops may return a larger type, that's why we cast explicitly. |
| michael@0 | 90 | // In C++, left bit shifts on signed values is undefined by the standard |
| michael@0 | 91 | // unless the shifted value is representable. |
| michael@0 | 92 | // Notice that signed-to-unsigned conversions are always well-defined in |
| michael@0 | 93 | // the standard as the value congruent to 2**n, as expected. By contrast, |
| michael@0 | 94 | // unsigned-to-signed is only well-defined if the value is representable. |
| michael@0 | 95 | static const IntegerType value = |
| michael@0 | 96 | IsSigned<IntegerType>::value |
| michael@0 | 97 | ? IntegerType(UnsignedIntegerType(1) << PosOfSignBit) |
| michael@0 | 98 | : IntegerType(0); |
| michael@0 | 99 | }; |
| michael@0 | 100 | |
| michael@0 | 101 | /** |
| michael@0 | 102 | * MaxValue returns the maximum value of the given integer type as a |
| michael@0 | 103 | * compile-time constant, which std::numeric_limits<IntegerType>::max() |
| michael@0 | 104 | * cannot do in c++98. |
| michael@0 | 105 | */ |
| michael@0 | 106 | template<typename IntegerType> |
| michael@0 | 107 | struct MaxValue |
| michael@0 | 108 | { |
| michael@0 | 109 | static_assert(IsIntegral<IntegerType>::value, "MaxValue is only for integral types"); |
| michael@0 | 110 | |
| michael@0 | 111 | // Tricksy, but covered by the CheckedInt unit test. |
| michael@0 | 112 | // Relies on the type of MinValue<IntegerType>::value |
| michael@0 | 113 | // being IntegerType. |
| michael@0 | 114 | static const IntegerType value = ~MinValue<IntegerType>::value; |
| michael@0 | 115 | }; |
| michael@0 | 116 | |
| michael@0 | 117 | } // namespace mozilla |
| michael@0 | 118 | |
| michael@0 | 119 | #endif // mozilla_IntegerTypeTraits_h |
