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      1 // Copyright (c) 2011 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 // This is an internal class that handles the address of a cache record.
      6 // See net/disk_cache/disk_cache.h for the public interface of the cache.
      7 
      8 #ifndef NET_DISK_CACHE_ADDR_H_
      9 #define NET_DISK_CACHE_ADDR_H_
     10 #pragma once
     11 
     12 #include "net/disk_cache/disk_format.h"
     13 
     14 namespace disk_cache {
     15 
     16 enum FileType {
     17   EXTERNAL = 0,
     18   RANKINGS = 1,
     19   BLOCK_256,
     20   BLOCK_1K,
     21   BLOCK_4K,
     22 };
     23 
     24 const int kMaxBlockSize = 4096 * 4;
     25 const int kMaxBlockFile = 255;
     26 const int kMaxNumBlocks = 4;
     27 const int kFirstAdditionalBlockFile = 4;
     28 
     29 // Defines a storage address for a cache record
     30 //
     31 // Header:
     32 //   1000 0000 0000 0000 0000 0000 0000 0000 : initialized bit
     33 //   0111 0000 0000 0000 0000 0000 0000 0000 : file type
     34 //
     35 // File type values:
     36 //   0 = separate file on disk
     37 //   1 = rankings block file
     38 //   2 = 256 byte block file
     39 //   3 = 1k byte block file
     40 //   4 = 4k byte block file
     41 //
     42 // If separate file:
     43 //   0000 1111 1111 1111 1111 1111 1111 1111 : file#  0 - 268,435,456 (2^28)
     44 //
     45 // If block file:
     46 //   0000 1100 0000 0000 0000 0000 0000 0000 : reserved bits
     47 //   0000 0011 0000 0000 0000 0000 0000 0000 : number of contiguous blocks 1-4
     48 //   0000 0000 1111 1111 0000 0000 0000 0000 : file selector 0 - 255
     49 //   0000 0000 0000 0000 1111 1111 1111 1111 : block#  0 - 65,535 (2^16)
     50 class Addr {
     51  public:
     52   Addr() : value_(0) {}
     53   explicit Addr(CacheAddr address) : value_(address) {}
     54   Addr(FileType file_type, int max_blocks, int block_file, int index) {
     55     value_ = ((file_type << kFileTypeOffset) & kFileTypeMask) |
     56              (((max_blocks - 1) << kNumBlocksOffset) & kNumBlocksMask) |
     57              ((block_file << kFileSelectorOffset) & kFileSelectorMask) |
     58              (index  & kStartBlockMask) | kInitializedMask;
     59   }
     60 
     61   CacheAddr value() const { return value_; }
     62   void set_value(CacheAddr address) {
     63     value_ = address;
     64   }
     65 
     66   bool is_initialized() const {
     67     return (value_ & kInitializedMask) != 0;
     68   }
     69 
     70   bool is_separate_file() const {
     71     return (value_ & kFileTypeMask) == 0;
     72   }
     73 
     74   bool is_block_file() const {
     75     return !is_separate_file();
     76   }
     77 
     78   FileType file_type() const {
     79     return static_cast<FileType>((value_ & kFileTypeMask) >> kFileTypeOffset);
     80   }
     81 
     82   int FileNumber() const {
     83     if (is_separate_file())
     84       return value_ & kFileNameMask;
     85     else
     86       return ((value_ & kFileSelectorMask) >> kFileSelectorOffset);
     87   }
     88 
     89   int start_block() const;
     90   int num_blocks() const;
     91   bool SetFileNumber(int file_number);
     92   int BlockSize() const {
     93     return BlockSizeForFileType(file_type());
     94   }
     95 
     96   static int BlockSizeForFileType(FileType file_type) {
     97     switch (file_type) {
     98       case RANKINGS:
     99         return 36;
    100       case BLOCK_256:
    101         return 256;
    102       case BLOCK_1K:
    103         return 1024;
    104       case BLOCK_4K:
    105         return 4096;
    106       default:
    107         return 0;
    108     }
    109   }
    110 
    111   static FileType RequiredFileType(int size) {
    112     if (size < 1024)
    113       return BLOCK_256;
    114     else if (size < 4096)
    115       return BLOCK_1K;
    116     else if (size <= 4096 * 4)
    117       return BLOCK_4K;
    118     else
    119       return EXTERNAL;
    120   }
    121 
    122   // Returns true if this address looks like a valid one.
    123   bool SanityCheck() const;
    124 
    125  private:
    126   static const uint32 kInitializedMask    = 0x80000000;
    127   static const uint32 kFileTypeMask       = 0x70000000;
    128   static const uint32 kFileTypeOffset     = 28;
    129   static const uint32 kNumBlocksMask      = 0x03000000;
    130   static const uint32 kNumBlocksOffset    = 24;
    131   static const uint32 kFileSelectorMask   = 0x00ff0000;
    132   static const uint32 kFileSelectorOffset = 16;
    133   static const uint32 kStartBlockMask     = 0x0000FFFF;
    134   static const uint32 kFileNameMask       = 0x0FFFFFFF;
    135 
    136   CacheAddr value_;
    137 };
    138 
    139 }  // namespace disk_cache
    140 
    141 #endif  // NET_DISK_CACHE_ADDR_H_
    142