Ruby implementation of Sift3 strings distance much faster alternative to levenshtein distance

gistfile1.txt

# Ruby version of Siderite's fast and accurate string distance algorith described here:
#
# http://siderite.blogspot.com/2007/04/super-fast-and-accurate-string-distance.html
class StringTools
  def self.sift3distance(s1, s2, maxOffset, maxDistance)
    if (s1.try(:length) || 0) == 0
      return s2.try(:length) || 0
    end

    if (s2.try(:length) || 0) == 0
      return s1.length
    end

    if s1 == s2
      return 0
    end

    c1 = c2 = lcs = 0
    temporaryDistance = nil

    while (c1 < s1.length) && (c2 < s2.length)
      if s1[c1] == s2[c2]
        lcs += 1
      else
        if (c1<c2)
          c2=c1
        else
          c1=c2
        end
        maxOffset.times do |i|
          if ((c1 + i < s1.length) && (s1[c1 + i] == s2[c2]))
            c1 += i
            break
          end
          if ((c2 + i < s2.length) && (s1[c1] == s2[c2 + i]))
            c2 += i
            break
          end
        end
      end
      c1 += 1
      c2 += 1
      if maxDistance.present?
        temporaryDistance=(c1+c2)/1.5-lcs
        if (temporaryDistance>=maxDistance)
          return temporaryDistance.round
        end
      end
    end
    return ((s1.length + s2.length) / 1.5 - lcs).round
  end
end