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