Disk cache: First pass to add support for sparse entries....

net/disk_cache/bitmap.h

+// Copyright (c) 2009 The Chromium 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 NET_DISK_CACHE_BITMAP_H_
+#define NET_DISK_CACHE_BITMAP_H_
+
+#include <algorithm>
+
+#include "base/basictypes.h"
+
+namespace disk_cache {
+
+// This class provides support for simple maps of bits.
+class Bitmap {
+ public:
+  Bitmap() : map_(NULL), num_bits_(0), array_size_(0), alloc_(false) {}
+
+  // This constructor will allocate on a uint32 boundary. If |clear_bits| is
+  // false, the bitmap bits will not be initialized.
+  Bitmap(int num_bits, bool clear_bits)
+     : num_bits_(num_bits), array_size_(RequiredArraySize(num_bits)),
+       alloc_(true) {
+    map_ = new uint32[array_size_];
+
+    // Initialize all of the bits.
+    if (clear_bits)
+      Clear();
+  }
+
+  // Constructs a Bitmap with the actual storage provided by the caller. |map|
+  // has to be valid until this object destruction. |num_bits| is the number of
+  // bits in the bitmap, and |num_words| is the size of |map| in 32-bit words.
+  Bitmap(uint32* map, int num_bits, int num_words)
+     : map_(map), num_bits_(num_bits),
+       // If size is larger than necessary, trim because array_size_ is used
+       // as a bound by various methods.
+       array_size_(std::min(RequiredArraySize(num_bits), num_words)),
+       alloc_(false) {}
+
+  ~Bitmap() {
+    if (alloc_)
+      delete[] map_;
+  }
+
+  // Resizes the bitmap.
+  // If |num_bits| < Size(), the extra bits will be discarded.
+  // If |num_bits| > Size(), the extra bits will be filled with zeros if
+  // |clear_bits| is true.
+  // This object cannot be using memory provided during construction.
+  void Resize(int num_bits, bool clear_bits);
+
+  // Returns the number of bits in the bitmap.
+  int Size() const { return num_bits_; }
+
+  // Returns the number of 32-bit words in the bitmap.
+  int ArraySize() const { return array_size_; }
+
+  // Sets all the bits to true or false.
+  void SetAll(bool value) {
+    memset(map_, (value ? 0xFF : 0x00), array_size_ * sizeof(*map_));
+  }
+
+  // Clears all bits in the bitmap
+  void Clear() { SetAll(false); }
+
+  // Sets the value, gets the value or toggles the value of a given bit.
+  void Set(int index, bool value);
+  bool Get(int index) const;
+  void Toggle(int index);
+
+  // Directly sets an element of the internal map. Requires |array_index| <
+  // ArraySize();
+  void SetMapElement(int array_index, uint32 value);
+
+  // Gets an entry of the internal map. Requires array_index <
+  // ArraySize()
+  uint32 GetMapElement(int array_index) const;
+
+  // Directly sets the whole internal map. |size| is the number of 32-bit words
+  // to set from |map|. If  |size| > array_size(), it ignores the end of |map|.
+  void SetMap(const uint32* map, int size);
+
+  // Gets a pointer to the internal map.
+  const uint32* GetMap() const { return map_; }
+
+  // Sets a range of bits to |value|.
+  void SetRange(int begin, int end, bool value);
+
+  // Returns true if any bit between begin inclusive and end exclusive is set.
+  // 0 <= |begin| <= |end| <= Size() is required.
+  bool TestRange(int begin, int end, bool value) const;
+
+  // Scans bits starting at bit *|index|, looking for a bit set to |value|. If
+  // it finds that bit before reaching bit index |limit|, sets *|index| to the
+  // bit index and returns true. Otherwise returns false.
+  // Requires |limit| <= Size().
+  //
+  // Note that to use these methods in a loop you must increment the index
+  // after each use, as in:
+  //
+  //  for (int index = 0 ; map.FindNextBit(&index, limit, value) ; ++index) {
+  //    DoSomethingWith(index);
+  //  }
+  bool FindNextBit(int* index, int limit, bool value) const;
+
+  // Finds the first offset >= *|index| and < |limit| that has its bit set.
+  // See FindNextBit() for more info.
+  bool FindNextSetBitBeforeLimit(int* index, int limit) const {
+    return FindNextBit(index, limit, true);
+  }
+
+  // Finds the first offset >= *|index| that has its bit set.
+  // See FindNextBit() for more info.
+  bool FindNextSetBit(int *index) const {
+    return FindNextSetBitBeforeLimit(index, num_bits_);
+  }
+
+  // Scans bits starting at bit *|index|, looking for a bit set to |value|. If
+  // it finds that bit before reaching bit index |limit|, sets *|index| to the
+  // bit index and then counts the number of consecutive bits set to |value|
+  // (before reaching |limit|), and returns that count. If no bit is found
+  // returns 0. Requires |limit| <= Size().
+  int FindBits(int* index, int limit, bool value) const;
+
+  // Returns number of allocated words required for a bitmap of size |num_bits|.
+  static int RequiredArraySize(int num_bits) {
+    // Force at least one allocated word.
+    if (num_bits <= kIntBits)
+      return 1;
+
+    return (num_bits + kIntBits - 1) >> kLogIntBits;
+  }
+
+ private:
+  static const int kIntBits = sizeof(uint32) * 8;
+  static const int kLogIntBits = 5;  // 2^5 == 32 bits per word.
+
+  // Sets |len| bits from |start| to |value|. All the bits to be set should be
+  // stored in the same word, and len < kIntBits.
+  void SetWordBits(int start, int len, bool value);
+
+  uint32* map_;           // The bitmap.
+  int num_bits_;          // The upper bound of the bitmap.
+  int array_size_;        // The physical size (in uint32s) of the bitmap.
+  bool alloc_;            // Whether or not we allocated the memory.
+
+  DISALLOW_COPY_AND_ASSIGN(Bitmap);
+};
+
+}  // namespace disk_cache
+
+#endif  // NET_DISK_CACHE_BITMAP_H_