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Extend StringRef's edit-distance algorithm to permit an upper bound on the allowed edit distance
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@116867 91177308-0d34-0410-b5e6-96231b3b80d8
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@@ -142,11 +142,16 @@ namespace llvm {
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/// operation, rather than as two operations (an insertion and a
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/// removal).
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///
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/// \param MaxEditDistance If non-zero, the maximum edit distance that
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/// this routine is allowed to compute. If the edit distance will exceed
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/// that maximum, returns \c MaxEditDistance+1.
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///
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/// \returns the minimum number of character insertions, removals,
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/// or (if \p AllowReplacements is \c true) replacements needed to
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/// transform one of the given strings into the other. If zero,
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/// the strings are identical.
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unsigned edit_distance(StringRef Other, bool AllowReplacements = true);
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unsigned edit_distance(StringRef Other, bool AllowReplacements = true,
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unsigned MaxEditDistance = 0);
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/// str - Get the contents as an std::string.
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std::string str() const {
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@@ -68,7 +68,8 @@ int StringRef::compare_numeric(StringRef RHS) const {
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// Compute the edit distance between the two given strings.
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unsigned StringRef::edit_distance(llvm::StringRef Other,
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bool AllowReplacements) {
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bool AllowReplacements,
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unsigned MaxEditDistance) {
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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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@@ -94,6 +95,8 @@ unsigned StringRef::edit_distance(llvm::StringRef Other,
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for (size_type y = 1; y <= m; ++y) {
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current[0] = y;
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unsigned BestThisRow = current[0];
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for (size_type x = 1; x <= n; ++x) {
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if (AllowReplacements) {
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current[x] = min(previous[x-1] + ((*this)[y-1] == Other[x-1]? 0u:1u),
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@@ -103,8 +106,12 @@ unsigned StringRef::edit_distance(llvm::StringRef Other,
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if ((*this)[y-1] == Other[x-1]) current[x] = previous[x-1];
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else current[x] = min(current[x-1], previous[x]) + 1;
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}
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BestThisRow = min(BestThisRow, current[x]);
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}
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if (MaxEditDistance && BestThisRow > MaxEditDistance)
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return MaxEditDistance + 1;
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unsigned *tmp = current;
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current = previous;
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previous = tmp;
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