Disk cache v3: The main index table.

net/disk_cache/addr.h

Index: net/disk_cache/addr.h
===================================================================
--- net/disk_cache/addr.h	(revision 235026)
+++ net/disk_cache/addr.h	(working copy)
@@ -54,6 +54,18 @@
 //   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) {}
@@ -116,6 +128,11 @@
     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: