sync/internal_api/public/base/node_ordinal.h

   1 // Copyright 2012 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 SYNC_INTERNAL_API_PUBLIC_BASE_NODE_ORDINAL_H_
   6 #define SYNC_INTERNAL_API_PUBLIC_BASE_NODE_ORDINAL_H_
   7
   8 #include "base/basictypes.h"
   9 #include "sync/base/sync_export.h"
  10 #include "sync/internal_api/public/base/ordinal.h"
  11
  12 namespace syncer {
  13
  14 // A NodeOrdinal is an Ordinal whose internal value comes from the
  15 // ordinal_in_parent field of SyncEntity (see sync.proto).  It uses
  16 // the entire uint8 range for backwards compatibility with the old
  17 // int64-based positioning.
  18
  19 struct NodeOrdinalTraits {
  20   static const uint8 kZeroDigit = 0;
  21   static const uint8 kMaxDigit = kuint8max;
  22   static const size_t kMinLength = 8;
  23 };
  24
  25 typedef Ordinal<NodeOrdinalTraits> NodeOrdinal;
  26
  27 static_assert(static_cast<char>(NodeOrdinal::kZeroDigit) == '\x00',
  28               "NodeOrdinal has incorrect zero digit");
  29 static_assert(static_cast<char>(NodeOrdinal::kOneDigit) == '\x01',
  30               "NodeOrdinal has incorrect one digit");
  31 static_assert(static_cast<char>(NodeOrdinal::kMidDigit) == '\x80',
  32               "NodeOrdinal has incorrect mid digit");
  33 static_assert(static_cast<char>(NodeOrdinal::kMaxDigit) == '\xff',
  34               "NodeOrdinal has incorrect max digit");
  35 static_assert(NodeOrdinal::kMidDigitValue == 128,
  36               "NodeOrdinal has incorrect mid digit value");
  37 static_assert(NodeOrdinal::kMaxDigitValue == 255,
  38               "NodeOrdinal has incorrect max digit value");
  39 static_assert(NodeOrdinal::kRadix == 256,
  40               "NodeOrdinal has incorrect radix");
  41
  42 // Converts an int64 position (usually from the position_in_parent
  43 // field of SyncEntity) to a NodeOrdinal.  This transformation
  44 // preserves the ordering relation: a < b under integer ordering if
  45 // and only if Int64ToNodeOrdinal(a) < Int64ToNodeOrdinal(b).
  46 SYNC_EXPORT_PRIVATE NodeOrdinal Int64ToNodeOrdinal(int64 x);
  47
  48 // The inverse of Int64ToNodeOrdinal.  This conversion is, in general,
  49 // lossy: NodeOrdinals can have arbitrary fidelity, while numeric
  50 // positions contain only 64 bits of information (in fact, this is the
  51 // reason we've moved away from them).
  52 SYNC_EXPORT_PRIVATE int64 NodeOrdinalToInt64(const NodeOrdinal& ordinal);
  53
  54 }  // namespace syncer
  55
  56 #endif  // SYNC_INTERNAL_API_PUBLIC_BASE_NODE_ORDINAL_H_