Bahuvrihi external

Use of this adaptation of the rubinius Array#[] is slower than the current implementation by a few clicks.

  def [](one, two = nil)
    # Normalise the argument variants
    start, finish, count, simple, is_range = nil, nil, nil, false, false

    case one
    when Fixnum
      if two
        start, count = one, two
        return nil if count < 0       # No need to go further
      else
        start, finish, simple = one, one, true
      end
    when Range
      is_range = true
      start, finish = one.begin, one.end
    when nil
      raise TypeError, "no implicit conversion from nil to integer"
    else
      raise TypeError, "can't convert #{one.class} into Integer"
    end

    # so it only needs to be calculated once...
    total = self.length

    # Convert negative indices
    start += total if start < 0

    if simple
      return nil if start < 0 or start >= total
      return at(start)

    # ONE past end only, MRI compat
    elsif start == total
      return []

    elsif start < 0 or start >= total
      return nil
    end

    finish = (start + count - 1) if count    # For non-ranges
    finish += total if finish < 0
    finish -= 1 if is_range and one.exclude_end?

    # Going past the end is ignored (sort of)
    finish = (total - 1) if finish >= total

    if finish < 0
      return [] if is_range
      return nil
    end

    return [] if finish < start or count == 0
    read(finish-start+1, start)
  end