What are the best (portable) cross-platform arbitrary-precision math libraries? [closed]

GMP is the popular choice. Squeak Smalltalk has a very nice library, but it's written in Smalltalk.

You asked for relevant books or articles. The tricky part of bignums is long division. I recommend Per Brinch Hansen's paper Multiple-Length Division Revisited: A Tour of the Minefield.

Overall, he fastest general purpose arbitrary precision library is GMP. If you want to work with floating point values, look at the the MPFR library. MPFR is based on GMP.

Regarding native arbitrary precision support in other languages, Python uses its own implementation because of license, code size, and code portability reasons. The GMPY module lets Python access the GMP library.

See TTMath, a small templated header-only library free for personal and commercial use.

I've not compared arbitrary precision arithmetic libraries to each other myself, but people who do seem to have more or less uniformly settled on GMP. For what it's worth, the arbitrary precision integers in GHC Haskell and GNU Guile Scheme are both implemented using GMP, and the fastest implementation of the pidigits benchmark on the language shootout is based on GMP.

What about Pari? It’s built on top GMP and provides all the other goodies about number theory operations you’ll ever need (and many symbolic computation stuff).