rubyinline.rb

class MyTest
  def factorial(n)
    f = 1
    n.downto(2) { |x| f *= x }
    f
  end

  inline do |builder|
    builder.c "
      long factorial_c(int max) {
        int i=max, result=1;
        while (i >= 2) { result *= i--; }
          return result;
      }"
  end 
end