chromium/v8/src/base/bit-field.h

// Copyright 2019 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef V8_BASE_BIT_FIELD_H_
#define V8_BASE_BIT_FIELD_H_

#include <stdint.h>

#include <algorithm>

#include "src/base/macros.h"

namespace v8 {
namespace base {

// ----------------------------------------------------------------------------
// BitField is a help template for encoding and decode bitfield with
// unsigned content.
// Instantiate them via 'using', which is cheaper than deriving a new class:
// using MyBitField = base::BitField<MyEnum, 4, 2>;
// The BitField class is final to enforce this style over derivation.

template <class T, int shift, int size, class U = uint32_t>
class BitField final { … };

// ----------------------------------------------------------------------------
// BitFieldUnion can be used to combine two linear BitFields.
// So far only the static mask is computed. Encoding and decoding tbd.
// Can be used for example as a quick combined check:
//   `if (BitFieldUnion<BFA, BFB>::kMask & bitfield) ...`

template <typename A, typename B>
class BitFieldUnion final { … };

BitField8;

BitField16;

BitField64;

// Helper macros for defining a contiguous sequence of bit fields. Example:
// (backslashes at the ends of respective lines of this multi-line macro
// definition are omitted here to please the compiler)
//
// #define MAP_BIT_FIELD1(V, _)
//   V(IsAbcBit, bool, 1, _)
//   V(IsBcdBit, bool, 1, _)
//   V(CdeBits, int, 5, _)
//   V(DefBits, MutableMode, 1, _)
//
// DEFINE_BIT_FIELDS(MAP_BIT_FIELD1)
// or
// DEFINE_BIT_FIELDS_64(MAP_BIT_FIELD1)
//
#define DEFINE_BIT_FIELD_RANGE_TYPE(Name, Type, Size, _) …

#define DEFINE_BIT_RANGES(LIST_MACRO) …

#define DEFINE_BIT_FIELD_TYPE(Name, Type, Size, RangesName) …

#define DEFINE_BIT_FIELD_64_TYPE(Name, Type, Size, RangesName) …

#define DEFINE_BIT_FIELDS(LIST_MACRO) …

#define DEFINE_BIT_FIELDS_64(LIST_MACRO) …

// ----------------------------------------------------------------------------
// BitSetComputer is a help template for encoding and decoding information for
// a variable number of items in an array.
//
// To encode boolean data in a smi array you would use:
//  using BoolComputer = BitSetComputer<bool, 1, kSmiValueSize, uint32_t>;
//
template <class T, int kBitsPerItem, int kBitsPerWord, class U>
class BitSetComputer { … };

}  // namespace base
}  // namespace v8

#endif  // V8_BASE_BIT_FIELD_H_