Hello,
Finally my double-precision-Pd efforts resulted in code decent enough to be useful in practice. It's all documented on:
http://www.katjaas.nl/doubleprecision/doubleprecision.html
From there you can download a .zip with two .patch files to make vanilla Pd
0.43-0 double precision ready. In fact what you have is 'arbitrary-precision' code which can be built for single or double precision with the setting of a single definition in the API header m_pd.h. Test patches are included.
So far, I have tested on OSX and Linux. Remarkably, double precision Pd performance is comparable to current Pd on the Intel CPU's. The only drawback that I can think of is, it eats memory. This would be a bummer for Pd users doing Ableton style stuff with lots of soundfiles to be loaded into RAM. Krzysztof Czaja already warned me for this at Pd Con, but at the time I forgot a bit about the problems with loading soundfiles during a live session.
For me, as a precision freak, it is a delight to work with double precision Pd. Some examples are illustrated on mentioned webpage. Unfortunately, my music stuff needs Pd extended. I would be happy to continue the project.
Katja