1// Copyright (c) 2009 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#ifndef NET_DISK_CACHE_BITMAP_H_
6#define NET_DISK_CACHE_BITMAP_H_
7
8#include <algorithm>
9
10#include "base/basictypes.h"
11
12namespace disk_cache {
13
14// This class provides support for simple maps of bits.
15class Bitmap {
16 public:
17  Bitmap() : map_(NULL), num_bits_(0), array_size_(0), alloc_(false) {}
18
19  // This constructor will allocate on a uint32 boundary. If |clear_bits| is
20  // false, the bitmap bits will not be initialized.
21  Bitmap(int num_bits, bool clear_bits)
22     : num_bits_(num_bits), array_size_(RequiredArraySize(num_bits)),
23       alloc_(true) {
24    map_ = new uint32[array_size_];
25
26    // Initialize all of the bits.
27    if (clear_bits)
28      Clear();
29  }
30
31  // Constructs a Bitmap with the actual storage provided by the caller. |map|
32  // has to be valid until this object destruction. |num_bits| is the number of
33  // bits in the bitmap, and |num_words| is the size of |map| in 32-bit words.
34  Bitmap(uint32* map, int num_bits, int num_words)
35     : map_(map), num_bits_(num_bits),
36       // If size is larger than necessary, trim because array_size_ is used
37       // as a bound by various methods.
38       array_size_(std::min(RequiredArraySize(num_bits), num_words)),
39       alloc_(false) {}
40
41  ~Bitmap() {
42    if (alloc_)
43      delete[] map_;
44  }
45
46  // Resizes the bitmap.
47  // If |num_bits| < Size(), the extra bits will be discarded.
48  // If |num_bits| > Size(), the extra bits will be filled with zeros if
49  // |clear_bits| is true.
50  // This object cannot be using memory provided during construction.
51  void Resize(int num_bits, bool clear_bits);
52
53  // Returns the number of bits in the bitmap.
54  int Size() const { return num_bits_; }
55
56  // Returns the number of 32-bit words in the bitmap.
57  int ArraySize() const { return array_size_; }
58
59  // Sets all the bits to true or false.
60  void SetAll(bool value) {
61    memset(map_, (value ? 0xFF : 0x00), array_size_ * sizeof(*map_));
62  }
63
64  // Clears all bits in the bitmap
65  void Clear() { SetAll(false); }
66
67  // Sets the value, gets the value or toggles the value of a given bit.
68  void Set(int index, bool value);
69  bool Get(int index) const;
70  void Toggle(int index);
71
72  // Directly sets an element of the internal map. Requires |array_index| <
73  // ArraySize();
74  void SetMapElement(int array_index, uint32 value);
75
76  // Gets an entry of the internal map. Requires array_index <
77  // ArraySize()
78  uint32 GetMapElement(int array_index) const;
79
80  // Directly sets the whole internal map. |size| is the number of 32-bit words
81  // to set from |map|. If  |size| > array_size(), it ignores the end of |map|.
82  void SetMap(const uint32* map, int size);
83
84  // Gets a pointer to the internal map.
85  const uint32* GetMap() const { return map_; }
86
87  // Sets a range of bits to |value|.
88  void SetRange(int begin, int end, bool value);
89
90  // Returns true if any bit between begin inclusive and end exclusive is set.
91  // 0 <= |begin| <= |end| <= Size() is required.
92  bool TestRange(int begin, int end, bool value) const;
93
94  // Scans bits starting at bit *|index|, looking for a bit set to |value|. If
95  // it finds that bit before reaching bit index |limit|, sets *|index| to the
96  // bit index and returns true. Otherwise returns false.
97  // Requires |limit| <= Size().
98  //
99  // Note that to use these methods in a loop you must increment the index
100  // after each use, as in:
101  //
102  //  for (int index = 0 ; map.FindNextBit(&index, limit, value) ; ++index) {
103  //    DoSomethingWith(index);
104  //  }
105  bool FindNextBit(int* index, int limit, bool value) const;
106
107  // Finds the first offset >= *|index| and < |limit| that has its bit set.
108  // See FindNextBit() for more info.
109  bool FindNextSetBitBeforeLimit(int* index, int limit) const {
110    return FindNextBit(index, limit, true);
111  }
112
113  // Finds the first offset >= *|index| that has its bit set.
114  // See FindNextBit() for more info.
115  bool FindNextSetBit(int *index) const {
116    return FindNextSetBitBeforeLimit(index, num_bits_);
117  }
118
119  // Scans bits starting at bit *|index|, looking for a bit set to |value|. If
120  // it finds that bit before reaching bit index |limit|, sets *|index| to the
121  // bit index and then counts the number of consecutive bits set to |value|
122  // (before reaching |limit|), and returns that count. If no bit is found
123  // returns 0. Requires |limit| <= Size().
124  int FindBits(int* index, int limit, bool value) const;
125
126  // Returns number of allocated words required for a bitmap of size |num_bits|.
127  static int RequiredArraySize(int num_bits) {
128    // Force at least one allocated word.
129    if (num_bits <= kIntBits)
130      return 1;
131
132    return (num_bits + kIntBits - 1) >> kLogIntBits;
133  }
134
135 private:
136  static const int kIntBits = sizeof(uint32) * 8;
137  static const int kLogIntBits = 5;  // 2^5 == 32 bits per word.
138
139  // Sets |len| bits from |start| to |value|. All the bits to be set should be
140  // stored in the same word, and len < kIntBits.
141  void SetWordBits(int start, int len, bool value);
142
143  uint32* map_;           // The bitmap.
144  int num_bits_;          // The upper bound of the bitmap.
145  int array_size_;        // The physical size (in uint32s) of the bitmap.
146  bool alloc_;            // Whether or not we allocated the memory.
147
148  DISALLOW_COPY_AND_ASSIGN(Bitmap);
149};
150
151}  // namespace disk_cache
152
153#endif  // NET_DISK_CACHE_BITMAP_H_
154