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139 lines
3.6 KiB
C++
139 lines
3.6 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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/* Helpers to manipulate integer types that don't fit in TypeTraits.h */
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#ifndef mozilla_IntegerTypeTraits_h
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#define mozilla_IntegerTypeTraits_h
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#include "mozilla/TypeTraits.h"
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#include <stdint.h>
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namespace mozilla {
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namespace detail {
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/**
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* StdintTypeForSizeAndSignedness returns the stdint integer type
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* of given size (can be 1, 2, 4 or 8) and given signedness
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* (false means unsigned, true means signed).
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*/
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template<size_t Size, bool Signedness>
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struct StdintTypeForSizeAndSignedness;
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template<>
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struct StdintTypeForSizeAndSignedness<1, true>
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{
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typedef int8_t Type;
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};
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template<>
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struct StdintTypeForSizeAndSignedness<1, false>
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{
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typedef uint8_t Type;
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};
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template<>
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struct StdintTypeForSizeAndSignedness<2, true>
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{
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typedef int16_t Type;
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};
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template<>
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struct StdintTypeForSizeAndSignedness<2, false>
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{
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typedef uint16_t Type;
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};
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template<>
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struct StdintTypeForSizeAndSignedness<4, true>
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{
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typedef int32_t Type;
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};
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template<>
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struct StdintTypeForSizeAndSignedness<4, false>
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{
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typedef uint32_t Type;
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};
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template<>
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struct StdintTypeForSizeAndSignedness<8, true>
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{
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typedef int64_t Type;
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};
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template<>
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struct StdintTypeForSizeAndSignedness<8, false>
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{
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typedef uint64_t Type;
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};
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} // namespace detail
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template<size_t Size>
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struct UnsignedStdintTypeForSize
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: detail::StdintTypeForSizeAndSignedness<Size, false>
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{};
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template<typename IntegerType>
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struct PositionOfSignBit
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{
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static_assert(IsIntegral<IntegerType>::value,
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"PositionOfSignBit is only for integral types");
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// 8 here should be CHAR_BIT from limits.h, but the world has moved on.
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static const size_t value = 8 * sizeof(IntegerType) - 1;
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};
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/**
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* MinValue returns the minimum value of the given integer type as a
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* compile-time constant, which std::numeric_limits<IntegerType>::min()
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* cannot do in c++98.
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*/
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template<typename IntegerType>
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struct MinValue
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{
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private:
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static_assert(IsIntegral<IntegerType>::value,
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"MinValue is only for integral types");
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typedef typename MakeUnsigned<IntegerType>::Type UnsignedIntegerType;
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static const size_t PosOfSignBit = PositionOfSignBit<IntegerType>::value;
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public:
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// Bitwise ops may return a larger type, that's why we cast explicitly.
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// In C++, left bit shifts on signed values is undefined by the standard
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// unless the shifted value is representable.
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// Notice that signed-to-unsigned conversions are always well-defined in
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// the standard as the value congruent to 2**n, as expected. By contrast,
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// unsigned-to-signed is only well-defined if the value is representable.
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static const IntegerType value =
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IsSigned<IntegerType>::value
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? IntegerType(UnsignedIntegerType(1) << PosOfSignBit)
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: IntegerType(0);
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};
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/**
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* MaxValue returns the maximum value of the given integer type as a
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* compile-time constant, which std::numeric_limits<IntegerType>::max()
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* cannot do in c++98.
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*/
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template<typename IntegerType>
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struct MaxValue
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{
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static_assert(IsIntegral<IntegerType>::value,
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"MaxValue is only for integral types");
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// Tricksy, but covered by the CheckedInt unit test.
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// Relies on the type of MinValue<IntegerType>::value
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// being IntegerType.
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static const IntegerType value = ~MinValue<IntegerType>::value;
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};
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} // namespace mozilla
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#endif // mozilla_IntegerTypeTraits_h
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