What arbitrary-precision integers (and or rationals) library are there for compilers running on Microsoft Windows, and which would you recommend?
Please state licens
Best bignum library to solve Project Euler problems in C++ ?
OpenSSL BN type. BSD-style license, pretty sure it's available for windows.
I have not used it, so I'm pointing you here blind:
LibTomMath by Tom St Denis: http://libtom.org/
Public Domain license. Website mentions that the library builds out of the box with GCC 2.95 [and up] as well as Visual C++ v6.00 [with SP5] without configuration.
A companion book is available: http://www.amazon.com/dp/1597491128
GMP.
LGPL. Standard download from official website is designed for GCC. VC++ port is available from here.