1/*
2 * Copyright (C) 2014 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#ifndef ART_RUNTIME_BASE_BIT_FIELD_H_
18#define ART_RUNTIME_BASE_BIT_FIELD_H_
19
20#include "globals.h"
21#include "logging.h"
22
23namespace art {
24
25static constexpr uintptr_t kUintPtrTOne = 1U;
26
27// BitField is a template for encoding and decoding a bit field inside
28// an unsigned machine word.
29template<typename T, size_t kPosition, size_t kSize>
30class BitField {
31 public:
32  typedef T value_type;
33  static constexpr size_t position = kPosition;
34  static constexpr size_t size = kSize;
35
36  static_assert(position < sizeof(uintptr_t) * kBitsPerByte, "Invalid position.");
37  static_assert(size != 0u, "Invalid size.");
38  static_assert(size <= sizeof(uintptr_t) * kBitsPerByte, "Invalid size.");
39  static_assert(size + position <= sizeof(uintptr_t) * kBitsPerByte, "Invalid position + size.");
40
41  // Tells whether the provided value fits into the bit field.
42  static bool IsValid(T value) {
43    return (static_cast<uintptr_t>(value) & ~((kUintPtrTOne << size) - 1)) == 0;
44  }
45
46  // Returns a uword mask of the bit field.
47  static uintptr_t Mask() {
48    return (kUintPtrTOne << size) - 1;
49  }
50
51  // Returns a uword mask of the bit field which can be applied directly to
52  // the raw unshifted bits.
53  static uintptr_t MaskInPlace() {
54    return ((kUintPtrTOne << size) - 1) << position;
55  }
56
57  // Returns the shift count needed to right-shift the bit field to
58  // the least-significant bits.
59  static int Shift() {
60    return position;
61  }
62
63  // Returns the size of the bit field.
64  static int BitSize() {
65    return size;
66  }
67
68  // Returns a uword with the bit field value encoded.
69  static uintptr_t Encode(T value) {
70    DCHECK(IsValid(value));
71    return static_cast<uintptr_t>(value) << position;
72  }
73
74  // Extracts the bit field from the value.
75  static T Decode(uintptr_t value) {
76    return static_cast<T>((value >> position) & ((kUintPtrTOne << size) - 1));
77  }
78
79  // Returns a uword with the bit field value encoded based on the
80  // original value. Only the bits corresponding to this bit field
81  // will be changed.
82  static uintptr_t Update(T value, uintptr_t original) {
83    DCHECK(IsValid(value));
84    return (static_cast<uintptr_t>(value) << position) |
85        (~MaskInPlace() & original);
86  }
87};
88
89}  // namespace art
90
91#endif  // ART_RUNTIME_BASE_BIT_FIELD_H_
92