LLVM  3.7.0
edit_distance.h
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1 //===-- llvm/ADT/edit_distance.h - Array edit distance function --- C++ -*-===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file defines a Levenshtein distance function that works for any two
11 // sequences, with each element of each sequence being analogous to a character
12 // in a string.
13 //
14 //===----------------------------------------------------------------------===//
15 
16 #ifndef LLVM_ADT_EDIT_DISTANCE_H
17 #define LLVM_ADT_EDIT_DISTANCE_H
18 
19 #include "llvm/ADT/ArrayRef.h"
20 #include <algorithm>
21 #include <memory>
22 
23 namespace llvm {
24 
25 /// \brief Determine the edit distance between two sequences.
26 ///
27 /// \param FromArray the first sequence to compare.
28 ///
29 /// \param ToArray the second sequence to compare.
30 ///
31 /// \param AllowReplacements whether to allow element replacements (change one
32 /// element into another) as a single operation, rather than as two operations
33 /// (an insertion and a removal).
34 ///
35 /// \param MaxEditDistance If non-zero, the maximum edit distance that this
36 /// routine is allowed to compute. If the edit distance will exceed that
37 /// maximum, returns \c MaxEditDistance+1.
38 ///
39 /// \returns the minimum number of element insertions, removals, or (if
40 /// \p AllowReplacements is \c true) replacements needed to transform one of
41 /// the given sequences into the other. If zero, the sequences are identical.
42 template<typename T>
43 unsigned ComputeEditDistance(ArrayRef<T> FromArray, ArrayRef<T> ToArray,
44  bool AllowReplacements = true,
45  unsigned MaxEditDistance = 0) {
46  // The algorithm implemented below is the "classic"
47  // dynamic-programming algorithm for computing the Levenshtein
48  // distance, which is described here:
49  //
50  // http://en.wikipedia.org/wiki/Levenshtein_distance
51  //
52  // Although the algorithm is typically described using an m x n
53  // array, only one row plus one element are used at a time, so this
54  // implementation just keeps one vector for the row. To update one entry,
55  // only the entries to the left, top, and top-left are needed. The left
56  // entry is in Row[x-1], the top entry is what's in Row[x] from the last
57  // iteration, and the top-left entry is stored in Previous.
58  typename ArrayRef<T>::size_type m = FromArray.size();
59  typename ArrayRef<T>::size_type n = ToArray.size();
60 
61  const unsigned SmallBufferSize = 64;
62  unsigned SmallBuffer[SmallBufferSize];
63  std::unique_ptr<unsigned[]> Allocated;
64  unsigned *Row = SmallBuffer;
65  if (n + 1 > SmallBufferSize) {
66  Row = new unsigned[n + 1];
67  Allocated.reset(Row);
68  }
69 
70  for (unsigned i = 1; i <= n; ++i)
71  Row[i] = i;
72 
73  for (typename ArrayRef<T>::size_type y = 1; y <= m; ++y) {
74  Row[0] = y;
75  unsigned BestThisRow = Row[0];
76 
77  unsigned Previous = y - 1;
78  for (typename ArrayRef<T>::size_type x = 1; x <= n; ++x) {
79  int OldRow = Row[x];
80  if (AllowReplacements) {
81  Row[x] = std::min(
82  Previous + (FromArray[y-1] == ToArray[x-1] ? 0u : 1u),
83  std::min(Row[x-1], Row[x])+1);
84  }
85  else {
86  if (FromArray[y-1] == ToArray[x-1]) Row[x] = Previous;
87  else Row[x] = std::min(Row[x-1], Row[x]) + 1;
88  }
89  Previous = OldRow;
90  BestThisRow = std::min(BestThisRow, Row[x]);
91  }
92 
93  if (MaxEditDistance && BestThisRow > MaxEditDistance)
94  return MaxEditDistance + 1;
95  }
96 
97  unsigned Result = Row[n];
98  return Result;
99 }
100 
101 } // End llvm namespace
102 
103 #endif
unsigned ComputeEditDistance(ArrayRef< T > FromArray, ArrayRef< T > ToArray, bool AllowReplacements=true, unsigned MaxEditDistance=0)
Determine the edit distance between two sequences.
Definition: edit_distance.h:43
Number of individual test Apply this number of consecutive mutations to each input exit after the first new interesting input is found the minimized corpus is saved into the first input directory Number of jobs to run If min(jobs, NumberOfCpuCores()/2)\" is used.") FUZZER_FLAG_INT(reload
ArrayRef - Represent a constant reference to an array (0 or more elements consecutively in memory)...
Definition: ArrayRef.h:31
size_t size() const
size - Get the array size.
Definition: ArrayRef.h:134
size_t size_type
Definition: ArrayRef.h:35