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      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 COMPILE_ASSERT(static_cast<char>(NodeOrdinal::kZeroDigit) == '\x00',
     28                NodeOrdinalHasCorrectZeroDigit);
     29 COMPILE_ASSERT(static_cast<char>(NodeOrdinal::kOneDigit) == '\x01',
     30                NodeOrdinalHasCorrectOneDigit);
     31 COMPILE_ASSERT(static_cast<char>(NodeOrdinal::kMidDigit) == '\x80',
     32                NodeOrdinalHasCorrectMidDigit);
     33 COMPILE_ASSERT(static_cast<char>(NodeOrdinal::kMaxDigit) == '\xff',
     34                NodeOrdinalHasCorrectMaxDigit);
     35 COMPILE_ASSERT(NodeOrdinal::kMidDigitValue == 128,
     36                NodeOrdinalHasCorrectMidDigitValue);
     37 COMPILE_ASSERT(NodeOrdinal::kMaxDigitValue == 255,
     38                NodeOrdinalHasCorrectMaxDigitValue);
     39 COMPILE_ASSERT(NodeOrdinal::kRadix == 256,
     40                NodeOrdinalHasCorrectRadix);
     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_
     57