xrc (exact reals in C) This is an implementation of lazy exact real arithmetic in C. It is an alternative to multiple-precision floating-point codes. An important distinction is that in multiple-precision floating-point, one sets the precision before starting a computation, and then one cannot be sure of the final result. Interval arithmetic is an improvement on this, but still not an ideal solution because if the final interval is larger than desired, there is no simple way to restart the computation at higher precision. By constrast, in exact real arithmetic no precision level is set in advance, and no computation takes place until a final request takes place for some output. I have previously developed similar codes in python and C++. This new C version is faster, more portable, and easier to use. (Source: http://www.mpfr.org/)