Disk cache v3: The main index table.

net/disk_cache/addr.h

 // Copyright (c) 2012 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.
 
 // This is an internal class that handles the address of a cache record.
 // See net/disk_cache/disk_cache.h for the public interface of the cache.
 
 #ifndef NET_DISK_CACHE_ADDR_H_
 #define NET_DISK_CACHE_ADDR_H_
 
@@ skipping 36 matching lines @@
 //   7 = evicted entries block file
 //
 // If separate file:
 //   0000 1111 1111 1111 1111 1111 1111 1111 : file#  0 - 268,435,456 (2^28)
 //
 // If block file:
 //   0000 1100 0000 0000 0000 0000 0000 0000 : reserved bits
 //   0000 0011 0000 0000 0000 0000 0000 0000 : number of contiguous blocks 1-4
 //   0000 0000 1111 1111 0000 0000 0000 0000 : file selector 0 - 255
 //   0000 0000 0000 0000 1111 1111 1111 1111 : block#  0 - 65,535 (2^16)
+//
+// Note that an Addr can be used to "point" to a variety of different objects,
+// from a given type of entry to random blobs of data. Conceptually, an Addr is
+// just a number that someone can inspect to find out how to locate the desired
+// record. Most users will not care about the specific bits inside Addr, for
+// example, what parts of it point to a file number; only the code that has to
+// select a specific file would care about those specific bits.
+//
+// From a general point of view, an Addr has a total capacity of 2^24 entities,
+// in that it has 24 bits that can identify individual records. Note that the
+// address space is bigger for independent files (2^28), but that would not be
+// the general case.
 class NET_EXPORT_PRIVATE Addr {
  public:
   Addr() : value_(0) {}
   explicit Addr(CacheAddr address) : value_(address) {}
   Addr(FileType file_type, int max_blocks, int block_file, int index) {
     value_ = ((file_type << kFileTypeOffset) & kFileTypeMask) |
              (((max_blocks - 1) << kNumBlocksOffset) & kNumBlocksMask) |
              ((block_file << kFileSelectorOffset) & kFileSelectorMask) |
              (index  & kStartBlockMask) | kInitializedMask;
   }
@@ skipping 42 matching lines @@
   }
 
   static Addr FromEntryAddress(uint32 value) {
     return Addr(kInitializedMask + (BLOCK_ENTRIES << kFileTypeOffset) + value);
   }
 
   static Addr FromEvictedAddress(uint32 value) {
     return Addr(kInitializedMask + (BLOCK_EVICTED << kFileTypeOffset) + value);
   }
 
+  // Returns the part of the address that could be stored by the index.
+  uint32 ToIndexEntryAddress() const {
+    return value_ & (kFileSelectorMask | kStartBlockMask);
+  }
+
   static int BlockSizeForFileType(FileType file_type) {
     switch (file_type) {
       case RANKINGS:
         return 36;
       case BLOCK_256:
         return 256;
       case BLOCK_1K:
         return 1024;
       case BLOCK_4K:
         return 4096;
@@ skipping 46 matching lines @@
   static const uint32 kFileSelectorOffset = 16;
   static const uint32 kStartBlockMask     = 0x0000FFFF;
   static const uint32 kFileNameMask       = 0x0FFFFFFF;
 
   CacheAddr value_;
 };
 
 }  // namespace disk_cache
 
 #endif  // NET_DISK_CACHE_ADDR_H_