[llvm-commits] [llvm] r92309 - in /llvm/trunk: include/llvm/ADT/StringRef.h lib/Support/StringRef.cpp

[Daniel Dunbar]

On Wed, Dec 30, 2009 at 9:23 AM, Douglas Gregor <dgregor at apple.com> wrote:
> Author: dgregor
> Date: Wed Dec 30 11:23:44 2009
> New Revision: 92309
>
> URL: http://llvm.org/viewvc/llvm-project?rev=92309&view=rev
> Log:
> Implement edit distance for StringRef

Nice! Can this use SmallVector instead of vector, and get a unittest?

 - Daniel

> Modified:
>    llvm/trunk/include/llvm/ADT/StringRef.h
>    llvm/trunk/lib/Support/StringRef.cpp
>
> Modified: llvm/trunk/include/llvm/ADT/StringRef.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/StringRef.h?rev=92309&r1=92308&r2=92309&view=diff
>
> ==============================================================================
> --- llvm/trunk/include/llvm/ADT/StringRef.h (original)
> +++ llvm/trunk/include/llvm/ADT/StringRef.h Wed Dec 30 11:23:44 2009
> @@ -133,6 +133,22 @@
>     /// compare_lower - Compare two strings, ignoring case.
>     int compare_lower(StringRef RHS) const;
>
> +    /// \brief Determine the edit distance between this string and another
> +    /// string.
> +    ///
> +    /// \param Other the string to compare this string against.
> +    ///
> +    /// \param AllowReplacements whether to allow character
> +    /// replacements (change one character into another) as a single
> +    /// operation, rather than as two operations (an insertion and a
> +    /// removal).
> +    ///
> +    /// \returns the minimum number of character insertions, removals,
> +    /// or (if \p AllowReplacements is \c true) replacements needed to
> +    /// transform one of the given strings into the other. If zero,
> +    /// the strings are identical.
> +    unsigned edit_distance(StringRef Other, bool AllowReplacements = true);
> +
>     /// str - Get the contents as an std::string.
>     std::string str() const { return std::string(Data, Length); }
>
>
> Modified: llvm/trunk/lib/Support/StringRef.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/StringRef.cpp?rev=92309&r1=92308&r2=92309&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/Support/StringRef.cpp (original)
> +++ llvm/trunk/lib/Support/StringRef.cpp Wed Dec 30 11:23:44 2009
> @@ -8,6 +8,7 @@
>  //===----------------------------------------------------------------------===//
>
>  #include "llvm/ADT/StringRef.h"
> +#include <vector>
>  using namespace llvm;
>
>  // MSVC emits references to this into the translation units which reference it.
> @@ -35,6 +36,36 @@
>   return Length < RHS.Length ? -1 : 1;
>  }
>
> +/// \brief Compute the edit distance between the two given strings.
> +unsigned StringRef::edit_distance(llvm::StringRef Other,
> +                                  bool AllowReplacements) {
> +  size_type m = size();
> +  size_type n = Other.size();
> +
> +  std::vector<unsigned> previous(n+1, 0);
> +  for (std::vector<unsigned>::size_type i = 0; i <= n; ++i)
> +    previous[i] = i;
> +
> +  std::vector<unsigned> current(n+1, 0);
> +  for (size_type y = 1; y <= m; ++y) {
> +    current.assign(n+1, 0);
> +    current[0] = y;
> +    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;
> +      }
> +    }
> +    current.swap(previous);
> +  }
> +
> +  return previous[n];
> +}
> +
>  //===----------------------------------------------------------------------===//
>  // String Searching
>  //===----------------------------------------------------------------------===//
>
>
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