Q: I need code for performing multiple precision arithmetic.
A: Some popular packages are the ``quad'' functions within the BSD Unix libc sources (ftp.uu.net, /systems/unix/bsd-sources/.../src/lib/libc/quad/*), the GNU MP library ``libmp'', the MIRACL package (see http://indigo.ie/~mscott/), the ``calc'' program by David Bell and Landon Curt Noll, and the old Unix libmp.a. See also questions 14.12 and 18.16.
Software Solutions in C Sec. 17 pp. 343-454