BigDecimal performance

[Tim Buktu]

Hi,

now that BigInteger deals better with large numbers, it would be nice
for that to translate into an improvement in BigDecimal performance
because BigDecimal is essentially a wrapper around BigInteger.
Unfortunately, BigDecimal is still slower than BigInteger because it has
to scale and round.

I don't see a way to fix this without breaking the
BigDecimal=BigInteger*10^n paradigm, but it could be done by introducing
something like a BigFloat class that wraps a BigInteger such that
BigFloat=BigInteger*2^n. I would expect the code to be less complex than
BigDecimal because the only places it would have to deal with powers of
ten would be conversion from and to String or BigDecimal. It would also
be faster than BigDecimal for the same reason, but the downside is that
it wouldn't accurately represent decimal fractions (just like float and
double).

Is this something that would be beneficial in the real world?

I also did a little experiment to see how long a computation would take
using BigDecimals vs the same computation using fixed-point BigInteger
arithmetic. I wrote two programs that calculate pi to a million digits.
The BigInteger version took 3 minutes; the BigDecimal version took 28
minutes (both single-threaded).

Tim