  Here I propose C and C++ interfaces and experimental implementation for
twofolds arithmetic. I introduce twofolds in my previous article entitled
"Twofold fast arithmetic" for tracking floating-point inaccuracy. Testing
shows, plain C enables high-performance computing with twofolds. C++ interface
enables coding as easily as ordinary floating-point numbers. My goal is
convincing you to try twofolds; I think assuring accuracy of math computations
is worth its cost. Code and use examples available at my web site, references
inside.
