    # File lib/compass/sass_extensions/functions/math.rb, line 28
      def logarithm(number, base = e )
        assert_type number, :Number
        assert_type base, :Number
        raise Sass::SyntaxError, "base to logarithm must be unitless." unless base.unitless?

        result = Math.log(number.value, base.value) rescue Math.log(number.value) / Math.log(base.value)
        Sass::Script::Number.new(result, number.numerator_units, number.denominator_units)
      end