[gmx-developers] Posit-enablement of GROMACS

Theodore Omtzigt theo at stillwater-sc.com
Tue Jul 31 20:29:48 CEST 2018

On Tue, Jul 31, Mark Abraham wrote:

One of our supercomputer center customers want to enable GROMACS with this
> new number system, and I am looking for subject matter experts that we
> should work with to enable GROMACS with the C++ posit arithmetic library
> that has been developed for the posit-based hardware accelerators.

What advantage has that center identified?

Memory and MPI communication bandwidth.

Posits typically compete with IEEE floating point twice their size. So
32bit posits tend to beat 64bit doubles in terms of numerical accuracy.

Secondly, posits with their reproducibility create pure identity
transformations when using forward/inverse transforms. We have FFT/iFFT
kernels using16bit posits that beat 64bit double implementations in terms
of numerical accuracy.

The FFT in particular was the first kernel we were going to enable with
posits to improve the performance of the communication.

Given this additional information, do you think that they are mistaken in
thinking that posits would be a net benefit to performance?
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