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