The beginnings of a BSD licensed bignum library
wbhart.blogspot.com
wbhart.blogspot.com
The author appears to be planning a restart of the project, but that won't happen until next year: http://wbhart.blogspot.com/2011_10_01_archive.html
https://github.com/wbhart/mpir-fft
For the time being it is implemented against the MPIR bignum library. But once BSDNT is up to it I will install it in BSDNT.
If I don't want this to become a multi-decade effort I have to compromise somewhere. The particular compromise I make is that the library will initially compile with GCC only and will use inline assembly.