/*
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* Copyright (C) 2017 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef ART_LIBARTBASE_BASE_BIT_STRUCT_DETAIL_H_
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#define ART_LIBARTBASE_BASE_BIT_STRUCT_DETAIL_H_
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#include "bit_utils.h"
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#include "globals.h"
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#include <type_traits>
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// Implementation details for bit_struct.h
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// Not intended to be used stand-alone.
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namespace art {
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template <typename T>
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static constexpr size_t BitStructSizeOf();
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namespace detail {
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// Select the smallest uintX_t that will fit kBitSize bits.
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template <size_t kBitSize>
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struct MinimumTypeUnsignedHelper {
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using type =
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typename std::conditional<kBitSize == 0, void, // NOLINT [whitespace/operators] [3]
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typename std::conditional<kBitSize <= 8, uint8_t, // NOLINT [whitespace/operators] [3]
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typename std::conditional<kBitSize <= 16, uint16_t, // NOLINT [whitespace/operators] [3]
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typename std::conditional<kBitSize <= 32, uint32_t,
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typename std::conditional<kBitSize <= 64, uint64_t,
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typename std::conditional<kBitSize <= BitSizeOf<uintmax_t>(), uintmax_t,
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void>::type>::type>::type>::type>::type>::type;
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};
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// Select the smallest [u]intX_t that will fit kBitSize bits.
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// Automatically picks intX_t or uintX_t based on the sign-ness of T.
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template <typename T, size_t kBitSize>
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struct MinimumTypeHelper {
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using type_unsigned = typename MinimumTypeUnsignedHelper<kBitSize>::type;
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using type =
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typename std::conditional</* if */ std::is_signed<T>::value,
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/* then */ typename std::make_signed<type_unsigned>::type,
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/* else */ type_unsigned>::type;
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};
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// Denotes the beginning of a bit struct.
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//
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// This marker is required by the C++ standard in order to
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// have a "common initial sequence".
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//
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// See C++ 9.5.1 [class.union]:
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// If a standard-layout union contains several standard-layout structs that share a common
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// initial sequence ... it is permitted to inspect the common initial sequence of any of
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// standard-layout struct members.
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template <size_t kSize>
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struct DefineBitStructSize {
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private:
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typename MinimumTypeUnsignedHelper<kSize>::type _;
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};
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// Check if type "T" has a member called _ in it.
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template <typename T>
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struct HasUnderscoreField {
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private:
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using TrueT = std::integral_constant<bool, true>::type;
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using FalseT = std::integral_constant<bool, false>::type;
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template <typename C>
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static constexpr auto Test(void*) -> decltype(std::declval<C>()._, TrueT{});
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template <typename>
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static constexpr FalseT Test(...);
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public:
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static constexpr bool value = decltype(Test<T>(nullptr))::value;
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};
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// Infer the type of the member of &T::M.
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template <typename T, typename M>
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M GetMemberType(M T:: *);
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// Ensure the minimal type storage for 'T' matches its declared BitStructSizeOf.
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// Nominally used by the BITSTRUCT_DEFINE_END macro.
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template <typename T>
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static constexpr bool ValidateBitStructSize() {
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static_assert(std::is_union<T>::value, "T must be union");
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static_assert(std::is_standard_layout<T>::value, "T must be standard-layout");
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static_assert(HasUnderscoreField<T>::value, "T must have the _ DefineBitStructSize");
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const size_t kBitStructSizeOf = BitStructSizeOf<T>();
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static_assert(std::is_same<decltype(GetMemberType(&T::_)),
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DefineBitStructSize<kBitStructSizeOf>>::value,
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"T::_ must be a DefineBitStructSize of the same size");
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const size_t kExpectedSize = (BitStructSizeOf<T>() < kBitsPerByte)
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? kBitsPerByte
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: RoundUpToPowerOfTwo(kBitStructSizeOf);
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// Ensure no extra fields were added in between START/END.
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const size_t kActualSize = sizeof(T) * kBitsPerByte;
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return kExpectedSize == kActualSize;
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}
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} // namespace detail
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} // namespace art
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#endif // ART_LIBARTBASE_BASE_BIT_STRUCT_DETAIL_H_
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