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to reflect the new license. We understand that people may be surprised that we're moving the header entirely to discuss the new license. We checked this carefully with the Foundation's lawyer and we believe this is the correct approach. Essentially, all code in the project is now made available by the LLVM project under our new license, so you will see that the license headers include that license only. Some of our contributors have contributed code under our old license, and accordingly, we have retained a copy of our old license notice in the top-level files in each project and repository. llvm-svn: 351636
103 lines
3.6 KiB
C++
103 lines
3.6 KiB
C++
//===-- llvm/ADT/edit_distance.h - Array edit distance function --- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines a Levenshtein distance function that works for any two
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// sequences, with each element of each sequence being analogous to a character
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// in a string.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_ADT_EDIT_DISTANCE_H
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#define LLVM_ADT_EDIT_DISTANCE_H
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#include "llvm/ADT/ArrayRef.h"
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#include <algorithm>
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#include <memory>
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namespace llvm {
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/// Determine the edit distance between two sequences.
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///
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/// \param FromArray the first sequence to compare.
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///
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/// \param ToArray the second sequence to compare.
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///
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/// \param AllowReplacements whether to allow element replacements (change one
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/// element into another) as a single operation, rather than as two operations
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/// (an insertion and a removal).
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///
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/// \param MaxEditDistance If non-zero, the maximum edit distance that this
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/// routine is allowed to compute. If the edit distance will exceed that
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/// maximum, returns \c MaxEditDistance+1.
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///
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/// \returns the minimum number of element insertions, removals, or (if
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/// \p AllowReplacements is \c true) replacements needed to transform one of
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/// the given sequences into the other. If zero, the sequences are identical.
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template<typename T>
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unsigned ComputeEditDistance(ArrayRef<T> FromArray, ArrayRef<T> ToArray,
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bool AllowReplacements = true,
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unsigned MaxEditDistance = 0) {
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// The algorithm implemented below is the "classic"
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// dynamic-programming algorithm for computing the Levenshtein
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// distance, which is described here:
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//
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// http://en.wikipedia.org/wiki/Levenshtein_distance
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//
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// Although the algorithm is typically described using an m x n
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// array, only one row plus one element are used at a time, so this
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// implementation just keeps one vector for the row. To update one entry,
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// only the entries to the left, top, and top-left are needed. The left
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// entry is in Row[x-1], the top entry is what's in Row[x] from the last
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// iteration, and the top-left entry is stored in Previous.
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typename ArrayRef<T>::size_type m = FromArray.size();
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typename ArrayRef<T>::size_type n = ToArray.size();
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const unsigned SmallBufferSize = 64;
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unsigned SmallBuffer[SmallBufferSize];
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std::unique_ptr<unsigned[]> Allocated;
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unsigned *Row = SmallBuffer;
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if (n + 1 > SmallBufferSize) {
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Row = new unsigned[n + 1];
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Allocated.reset(Row);
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}
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for (unsigned i = 1; i <= n; ++i)
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Row[i] = i;
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for (typename ArrayRef<T>::size_type y = 1; y <= m; ++y) {
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Row[0] = y;
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unsigned BestThisRow = Row[0];
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unsigned Previous = y - 1;
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for (typename ArrayRef<T>::size_type x = 1; x <= n; ++x) {
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int OldRow = Row[x];
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if (AllowReplacements) {
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Row[x] = std::min(
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Previous + (FromArray[y-1] == ToArray[x-1] ? 0u : 1u),
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std::min(Row[x-1], Row[x])+1);
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}
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else {
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if (FromArray[y-1] == ToArray[x-1]) Row[x] = Previous;
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else Row[x] = std::min(Row[x-1], Row[x]) + 1;
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}
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Previous = OldRow;
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BestThisRow = std::min(BestThisRow, Row[x]);
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}
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if (MaxEditDistance && BestThisRow > MaxEditDistance)
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return MaxEditDistance + 1;
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}
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unsigned Result = Row[n];
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return Result;
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}
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} // End llvm namespace
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#endif
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