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Add function for computing the edit distance of two arrays.

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Accomplished by moving the body of StringRef::edit_distance into
a separate function that accepts two ArrayRefs, and making
StringRef::edit_distance a wrapper around the new function.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@150621 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Kaelyn Uhrain
2012-02-15 22:13:07 +00:00
parent 68c36e0c26
commit 01d53ec176
2 changed files with 107 additions and 51 deletions
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56
lib/Support/StringRef.cpp
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@@ -10,6 +10,7 @@
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/APInt.h"
#include "llvm/ADT/OwningPtr.h"
#include "llvm/ADT/edit_distance.h"
#include <bitset>
using namespace llvm;
@@ -84,57 +85,10 @@ int StringRef::compare_numeric(StringRef RHS) const {
unsigned StringRef::edit_distance(llvm::StringRef Other,
bool AllowReplacements,
unsigned MaxEditDistance) {
// 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.
size_type m = size();
size_type n = Other.size();
const unsigned SmallBufferSize = 64;
unsigned SmallBuffer[SmallBufferSize];
llvm::OwningArrayPtr<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 (size_type y = 1; y <= m; ++y) {
current[0] = y;
unsigned BestThisRow = current[0];
for (size_type x = 1; x <= n; ++x) {
if (AllowReplacements) {
current[x] = min(previous[x-1] + ((*this)[y-1] == Other[x-1]? 0u:1u),
min(current[x-1], previous[x])+1);
}
else {
if ((*this)[y-1] == Other[x-1]) current[x] = previous[x-1];
else current[x] = min(current[x-1], previous[x]) + 1;
}
BestThisRow = min(BestThisRow, current[x]);
}
if (MaxEditDistance && BestThisRow > MaxEditDistance)
return MaxEditDistance + 1;
unsigned *tmp = current;
current = previous;
previous = tmp;
}
unsigned Result = previous[n];
return Result;
return llvm::ComputeEditDistance(
llvm::ArrayRef<char>(data(), size()),
llvm::ArrayRef<char>(Other.data(), Other.size()),
AllowReplacements, MaxEditDistance);
}
//===----------------------------------------------------------------------===//