Arbitrary Precision
MPFUN2015 is a Fortran arbitrary precision library by David H. Bailey. An archive of the source code can be found on his website here (note that I also have a mirror of the source at GitHub if you want to peruse it). This library seems to be one of the few freely-available production-ready arbitrary precision Fortran libraries available that I can find, although arbitrary precision Fortran code has existed for quite a while (e.g., see Reference 1 from 1971). MPFUN2015 is pretty easy to use, but I think could use a little bit of modernization.
See also
- L. C. Maximon, Fortran Program for Arbitrary Precision Arithmetic, National Bureau of Standards, NBS 10-563, April 1, 1971.
- D. H. Bailey, A Thread-Safe Arbitrary Precision Computation Package (Full Documentation), August 23, 2019.