class Sass::Util::MultibyteStringScanner

def pos=(n)
  @mb_last_pos = nil
  # We set position kind of a lot during parsing, so we want it to be as
  # efficient as possible. This is complicated by the fact that UTF-8 is a
  # variable-length encoding, so it's difficult to find the byte length that
  # corresponds to a given character length.
  #
  # Our heuristic here is to try to count the fewest possible characters. So
  # if the new position is close to the current one, just count the
  # characters between the two; if the new position is closer to the
  # beginning of the string, just count the characters from there.
  if @mb_pos - n < @mb_pos / 2
    # New position is close to old position
    byte_delta = @mb_pos > n ? -string[n...@mb_pos].bytesize : string[@mb_pos...n].bytesize
    super(byte_pos + byte_delta)
  else
    # New position is close to BOS
    super(string[0...n].bytesize)
  end
  @mb_pos = n
end