instance method get_confidence

# File actionmailer/lib/action_mailer/vendor/tmail-1.2.7/tmail/vendor/rchardet-1.3/lib/rchardet/latin1prober.rb, line 127
    def get_confidence
      if get_state() == ENotMe
        return 0.01
      end

      total = @_mFreqCounter.inject{|a,b| a+b} 
      if total < 0.01
        confidence = 0.0
      else
        confidence = (@_mFreqCounter[3] / total) - (@_mFreqCounter[1] * 20.0 / total)
      end
      if confidence < 0.0
        confidence = 0.0
      end
      # lower the confidence of latin1 so that other more accurate detector 
      # can take priority.
      confidence = confidence * 0.5
      return confidence
    end