| //===-- llvm/ADT/edit_distance.h - Array edit distance function --- C++ -*-===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This file defines a Levenshtein distance function that works for any two |
| // sequences, with each element of each sequence being analogous to a character |
| // in a string. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #ifndef LLVM_ADT_EDIT_DISTANCE_H |
| #define LLVM_ADT_EDIT_DISTANCE_H |
| |
| #include "llvm/ADT/ArrayRef.h" |
| #include <algorithm> |
| #include <memory> |
| |
| namespace llvm { |
| |
| /// \brief Determine the edit distance between two sequences. |
| /// |
| /// \param FromArray the first sequence to compare. |
| /// |
| /// \param ToArray the second sequence to compare. |
| /// |
| /// \param AllowReplacements whether to allow element replacements (change one |
| /// element into another) as a single operation, rather than as two operations |
| /// (an insertion and a removal). |
| /// |
| /// \param MaxEditDistance If non-zero, the maximum edit distance that this |
| /// routine is allowed to compute. If the edit distance will exceed that |
| /// maximum, returns \c MaxEditDistance+1. |
| /// |
| /// \returns the minimum number of element insertions, removals, or (if |
| /// \p AllowReplacements is \c true) replacements needed to transform one of |
| /// the given sequences into the other. If zero, the sequences are identical. |
| template<typename T> |
| unsigned ComputeEditDistance(ArrayRef<T> FromArray, ArrayRef<T> ToArray, |
| bool AllowReplacements = true, |
| unsigned MaxEditDistance = 0) { |
| // The algorithm implemented below is the "classic" |
| // dynamic-programming algorithm for computing the Levenshtein |
| // distance, which is described here: |
| // |
| // http://en.wikipedia.org/wiki/Levenshtein_distance |
| // |
| // Although the algorithm is typically described using an m x n |
| // array, only two rows are used at a time, so this implemenation |
| // just keeps two separate vectors for those two rows. |
| typename ArrayRef<T>::size_type m = FromArray.size(); |
| typename ArrayRef<T>::size_type n = ToArray.size(); |
| |
| const unsigned SmallBufferSize = 64; |
| unsigned SmallBuffer[SmallBufferSize]; |
| std::unique_ptr<unsigned[]> Allocated; |
| unsigned *Previous = SmallBuffer; |
| if (2*(n + 1) > SmallBufferSize) { |
| Previous = new unsigned [2*(n+1)]; |
| Allocated.reset(Previous); |
| } |
| unsigned *Current = Previous + (n + 1); |
| |
| for (unsigned i = 0; i <= n; ++i) |
| Previous[i] = i; |
| |
| for (typename ArrayRef<T>::size_type y = 1; y <= m; ++y) { |
| Current[0] = y; |
| unsigned BestThisRow = Current[0]; |
| |
| for (typename ArrayRef<T>::size_type x = 1; x <= n; ++x) { |
| if (AllowReplacements) { |
| Current[x] = std::min( |
| Previous[x-1] + (FromArray[y-1] == ToArray[x-1] ? 0u : 1u), |
| std::min(Current[x-1], Previous[x])+1); |
| } |
| else { |
| if (FromArray[y-1] == ToArray[x-1]) Current[x] = Previous[x-1]; |
| else Current[x] = std::min(Current[x-1], Previous[x]) + 1; |
| } |
| BestThisRow = std::min(BestThisRow, Current[x]); |
| } |
| |
| if (MaxEditDistance && BestThisRow > MaxEditDistance) |
| return MaxEditDistance + 1; |
| |
| unsigned *tmp = Current; |
| Current = Previous; |
| Previous = tmp; |
| } |
| |
| unsigned Result = Previous[n]; |
| return Result; |
| } |
| |
| } // End llvm namespace |
| |
| #endif |