Further BigInteger performance improvements

[Andrew Haley]

Alan Eliasen wrote:

>    From the queries I get, this is important to a lot of people.  The
> performance of BigInteger can be improved by tens or hundreds or
> thousands of times (or even more in the case of certain arguments of
> pow()), and should be done to make Java a more viable platform for numerics.
> 
>    This work has been in Sun's hands for a long time, and really needs
> to get into 1.7.

You give examples of the speedup for very large bignums, but you don't say
the size of numbers at which your approach becomes faster than the current
code.  Of course any asymptotic improvement helps with numbers that are
half a million decimal digits long, but where's the crossover?

Andrew.