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+// Copyright 2013 Google Inc. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//
+// Author: dsites@google.com (Dick Sites)
+//
+
+#ifndef UTIL_UTF8_OFFSETMAP_H_
+#define UTIL_UTF8_OFFSETMAP_H_
+
+#include <string>                       // for string
+#include "integral_types.h"             // for uint32
+
+// ***************************** OffsetMap **************************
+//
+// An OffsetMap object is a container for a mapping from offsets in one text
+// buffer A' to offsets in another text buffer A. It is most useful when A' is
+// built from A via substitutions that occasionally do not preserve byte length.
+//
+// A series of operators are used to build the correspondence map, then
+// calls can be made to map an offset in A' to an offset in A, or vice versa.
+// The map starts with offset 0 in A corresponding to offset 0 in A'.
+// The mapping is then built sequentially, adding on byte ranges that are
+// identical in A and A', byte ranges that are inserted in A', and byte ranges
+// that are deleted from A. All bytes beyond those specified when building the
+// map are assumed to correspond, i.e. a Copy(infinity) is assumed at the
+// end of the map.
+//
+// The internal data structure records positions at which bytes are added or
+// deleted. Using the map is O(1) when increasing the A' or A offset
+// monotonically, and O(n) when accessing random offsets, where n is the
+// number of differences.
+//
+
+namespace CLD2 {
+
+class OffsetMap {
+ public:
+  // Constructor, destructor
+  OffsetMap();
+  ~OffsetMap();
+
+  // Clear the map
+  void Clear();
+
+  // Add to  mapping from A to A', specifying how many next bytes correspond
+  // in A and A'
+  void Copy(int bytes);
+
+  // Add to mapping from A to A', specifying how many next bytes are
+  // inserted in A' while not advancing in A at all
+  void Insert(int bytes);
+
+  // Add to mapping from A to A', specifying how many next bytes are
+  // deleted from A while not advancing in A' at all
+  void Delete(int bytes);
+
+  // Print map to file, for debugging
+  void Printmap(const char* filename);
+
+  // [Finish building map,] Re-position to offset 0
+  // This call is optional; MapForward and MapBack finish building the map
+  // if necessary
+  void Reset();
+
+  // Map an offset in A' to the corresponding offset in A
+  int MapBack(int aprimeoffset);
+
+  // Map an offset in A to the corresponding offset in A'
+  int MapForward(int aoffset);
+
+  // h = ComposeOffsetMap(g, f), where f is a map from A to A', g is
+  // from A' to A'' and h is from A to A''.
+  //
+  // Note that g->MoveForward(f->MoveForward(aoffset)) always equals
+  // to h->MoveForward(aoffset), while
+  // f->MoveBack(g->MoveBack(aprimeprimeoffset)) doesn't always equals
+  // to h->MoveBack(aprimeprimeoffset). This happens when deletion in
+  // f and insertion in g are at the same place.  For example,
+  //
+  // A    1   2   3   4
+  //      ^   |  ^    ^
+  //      |   | /     |  f
+  //      v   vv      v
+  // A'   1'  2'      3'
+  //      ^   ^^      ^
+  //      |   | \     |  g
+  //      v   |  v    v
+  // A''  1'' 2'' 3'' 4''
+  //
+  // results in:
+  //
+  // A    1   2   3   4
+  //      ^   ^\  ^   ^
+  //      |   | \ |   |  h
+  //      v   |  vv   v
+  // A''  1'' 2'' 3'' 4''
+  //
+  // 2'' is mapped 3 in the former figure, while 2'' is mapped to 2 in
+  // the latter figure.
+  static void ComposeOffsetMap(OffsetMap* g, OffsetMap* f, OffsetMap* h);
+
+  // For debugging only; writes to stderr
+  void DumpWindow();
+
+  // For testing only -- force a mapping
+  void StuffIt(const std::string& diffs, int max_aoffset, int max_aprimeoffset);
+
+ private:
+  enum MapOp {PREFIX_OP, COPY_OP, INSERT_OP, DELETE_OP};
+
+  void Flush();
+  void FlushAll();
+  void MaybeFlushAll();
+  void Emit(MapOp op, int len);
+
+  void SetLeft();
+  void SetRight();
+
+  // Back up over previous range, 1..5 bytes
+  // Return subscript at the beginning of that. Pins at 0
+  int Backup(int sub);
+
+  // Parse next range, 1..5 bytes
+  // Return subscript just off the end of that
+  int ParseNext(int sub, MapOp* op, int* length);
+
+  // Parse previous range, 1..5 bytes
+  // Return current subscript
+  int ParsePrevious(int sub, MapOp* op, int* length);
+
+  void PrintPosition(const char* str);
+
+  bool MoveRight();     // Returns true if OK
+  bool MoveLeft();      // Returns true if OK
+  void DumpString();
+
+  // Copies insert operations from source to dest. Returns true if no
+  // other operations are found.
+  static bool CopyInserts(OffsetMap* source, OffsetMap* dest);
+
+  // Copies delete operations from source to dest. Returns true if no other
+  // operations are found.
+  static bool CopyDeletes(OffsetMap* source, OffsetMap* dest);
+
+  std::string diffs_;
+  MapOp pending_op_;
+  uint32 pending_length_;
+
+  // Offsets in the ranges below correspond to each other, with A' = A + diff
+  int next_diff_sub_;
+  int current_lo_aoffset_;
+  int current_hi_aoffset_;
+  int current_lo_aprimeoffset_;
+  int current_hi_aprimeoffset_;
+  int current_diff_;
+  int max_aoffset_;
+  int max_aprimeoffset_;
+};
+
+}  // namespace CLD2
+
+#endif  // UTIL_UTF8_OFFSETMAP_H_
+