libmpdecimal

[John Ralls]

On Jul 31, 2014, at 7:13 AM, Geert Janssens <info at kobaltwit.be> wrote:

> On Saturday 19 July 2014 11:53:37 John Ralls wrote:
> > The libmpdecimal branch now passes make check all the way through.
> > I've force-pushed a rebase on the latest master to
> > https://github.com/jralls/gnucash.git for anyone who'd like to play
> > with it.
> > 
> > Next step is to do some tuning to see how much I can shrink it while
> > getting full 64-bit coefficients (current tests limit it to 44-bits)
> > then profiling to see if there are any performance differences to
> > master.
> > 
> > Regards,
> > John Ralls
> > 
> > 
> > _______________________________________________
> > gnucash-devel mailing list
> > gnucash-devel at gnucash.org
> > https://lists.gnucash.org/mailman/listinfo/gnucash-devel
>  
> Nice! Keep up the good work.
>  
> I'm curious to hear about the performance difference. Hopefully the performance will be better :)

Libmpdecimal is about 25% slower as it is now, but I see some good optimization opportunities from the profile. I'm also looking at the Intel and GCC/ICU versions to see if they might prove faster, since mpdecimal is written specifically for Python and so has some extra overhead that doesn't seem to be present in the others.

The Intel version is particularly interesting because it uses a different encoding scheme and dispenses with contexts, both of which they claim afford much faster execution. Unfortunately their code is rather impenetrable and the documentation is sparse and difficult to understand. It also doesn't appear to expose an interface that can be used to extract a rational expression of the number, so it would require more code changes in the rest of GnuCash to be useable.

Removing the 44-bit clamp and increasing the range of the denominators from 10^6 to 10^9 passes all tests except test-lots, which fails from being unable to balance the lots in complex cases. I'm still debugging that.

Regards,
John Ralls