1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/mfbt/IntegerTypeTraits.h Wed Dec 31 06:09:35 2014 +0100
1.3 @@ -0,0 +1,119 @@
1.4 +/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
1.5 +/* vim: set ts=8 sts=2 et sw=2 tw=80: */
1.6 +/* This Source Code Form is subject to the terms of the Mozilla Public
1.7 + * License, v. 2.0. If a copy of the MPL was not distributed with this
1.8 + * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
1.9 +
1.10 +/* Helpers to manipulate integer types that don't fit in TypeTraits.h */
1.11 +
1.12 +#ifndef mozilla_IntegerTypeTraits_h
1.13 +#define mozilla_IntegerTypeTraits_h
1.14 +
1.15 +#include "mozilla/TypeTraits.h"
1.16 +#include <stdint.h>
1.17 +
1.18 +namespace mozilla {
1.19 +
1.20 +namespace detail {
1.21 +
1.22 +/**
1.23 + * StdintTypeForSizeAndSignedness returns the stdint integer type
1.24 + * of given size (can be 1, 2, 4 or 8) and given signedness
1.25 + * (false means unsigned, true means signed).
1.26 + */
1.27 +template<size_t Size, bool Signedness>
1.28 +struct StdintTypeForSizeAndSignedness;
1.29 +
1.30 +template<>
1.31 +struct StdintTypeForSizeAndSignedness<1, true>
1.32 +{ typedef int8_t Type; };
1.33 +
1.34 +template<>
1.35 +struct StdintTypeForSizeAndSignedness<1, false>
1.36 +{ typedef uint8_t Type; };
1.37 +
1.38 +template<>
1.39 +struct StdintTypeForSizeAndSignedness<2, true>
1.40 +{ typedef int16_t Type; };
1.41 +
1.42 +template<>
1.43 +struct StdintTypeForSizeAndSignedness<2, false>
1.44 +{ typedef uint16_t Type; };
1.45 +
1.46 +template<>
1.47 +struct StdintTypeForSizeAndSignedness<4, true>
1.48 +{ typedef int32_t Type; };
1.49 +
1.50 +template<>
1.51 +struct StdintTypeForSizeAndSignedness<4, false>
1.52 +{ typedef uint32_t Type; };
1.53 +
1.54 +template<>
1.55 +struct StdintTypeForSizeAndSignedness<8, true>
1.56 +{ typedef int64_t Type; };
1.57 +
1.58 +template<>
1.59 +struct StdintTypeForSizeAndSignedness<8, false>
1.60 +{ typedef uint64_t Type; };
1.61 +
1.62 +} // namespace detail
1.63 +
1.64 +template<size_t Size>
1.65 +struct UnsignedStdintTypeForSize
1.66 + : detail::StdintTypeForSizeAndSignedness<Size, false>
1.67 +{};
1.68 +
1.69 +template<typename IntegerType>
1.70 +struct PositionOfSignBit
1.71 +{
1.72 + static_assert(IsIntegral<IntegerType>::value, "PositionOfSignBit is only for integral types");
1.73 + // 8 here should be CHAR_BIT from limits.h, but the world has moved on.
1.74 + static const size_t value = 8 * sizeof(IntegerType) - 1;
1.75 +};
1.76 +
1.77 +/**
1.78 + * MinValue returns the minimum value of the given integer type as a
1.79 + * compile-time constant, which std::numeric_limits<IntegerType>::min()
1.80 + * cannot do in c++98.
1.81 + */
1.82 +template<typename IntegerType>
1.83 +struct MinValue
1.84 +{
1.85 + private:
1.86 + static_assert(IsIntegral<IntegerType>::value, "MinValue is only for integral types");
1.87 +
1.88 + typedef typename MakeUnsigned<IntegerType>::Type UnsignedIntegerType;
1.89 + static const size_t PosOfSignBit = PositionOfSignBit<IntegerType>::value;
1.90 +
1.91 + public:
1.92 + // Bitwise ops may return a larger type, that's why we cast explicitly.
1.93 + // In C++, left bit shifts on signed values is undefined by the standard
1.94 + // unless the shifted value is representable.
1.95 + // Notice that signed-to-unsigned conversions are always well-defined in
1.96 + // the standard as the value congruent to 2**n, as expected. By contrast,
1.97 + // unsigned-to-signed is only well-defined if the value is representable.
1.98 + static const IntegerType value =
1.99 + IsSigned<IntegerType>::value
1.100 + ? IntegerType(UnsignedIntegerType(1) << PosOfSignBit)
1.101 + : IntegerType(0);
1.102 +};
1.103 +
1.104 +/**
1.105 + * MaxValue returns the maximum value of the given integer type as a
1.106 + * compile-time constant, which std::numeric_limits<IntegerType>::max()
1.107 + * cannot do in c++98.
1.108 + */
1.109 +template<typename IntegerType>
1.110 +struct MaxValue
1.111 +{
1.112 + static_assert(IsIntegral<IntegerType>::value, "MaxValue is only for integral types");
1.113 +
1.114 + // Tricksy, but covered by the CheckedInt unit test.
1.115 + // Relies on the type of MinValue<IntegerType>::value
1.116 + // being IntegerType.
1.117 + static const IntegerType value = ~MinValue<IntegerType>::value;
1.118 +};
1.119 +
1.120 +} // namespace mozilla
1.121 +
1.122 +#endif // mozilla_IntegerTypeTraits_h
