high performance arbitrary precision arithmetic library for Java

 Apfloat is a high performance arbitrary precision arithmetic library.
 You can perform calculations with a precision of millions of digits with
 it. It's as simple to use as Java's BigDecimal or BigInteger classes,
 but performs a lot better with extreme precision numbers (more than a
 few hundred digits). Also, a full suite of mathematical functions for
 arbitrary precision numbers are available: all those existing in
 java.lang.Math and more.