module Math
  class << self
    # Standard in Ruby 1.9. See official documentation[http://ruby-doc.org/core-1.9/classes/Math.html]
    unless (log(2, 2) rescue false)
      def log_with_optional_base(numeric, base = Backports::Undefined)
        if base.equal?(Backports::Undefined)
          # Math.log(n) in 1.9.1 no longer accepts string arguments as it
          # did on 1.8.x, but we won't risk redefining existing behavior
          # when called with just one argument.
          log_without_optional_base(numeric)
        else
          # Math.log(n, b) in 1.9.1 does not accept string arguments:
          raise TypeError, "can't convert String into Float" if numeric.is_a?(String) || base.is_a?(String)
          log_without_optional_base(numeric) / log_without_optional_base(base)
        end
      end
      Backports.alias_method_chain self, :log, :optional_base
    end

    # Standard in Ruby 1.9. See official documentation[http://ruby-doc.org/core-1.9/classes/Math.html]
    def log2(numeric)
      log(numeric, 2)
    end unless method_defined? :log2
  end
end