Re: Performance question concerning chicken flonum vs "foreign flonum"

[Christian Himpe]

Christian Himpe schrieb am 2021-11-07:

> felix.winkelmann@bevuta.com schrieb am 2021-11-07:
> > > Dear Felix,
> > >
> > > Thank you for the patch. I built the current git head with your patch.
> > > After importing chicken.flonum, I get the following error when calling 
> > > fp*+:
> > >

> > I'm terribly sorry. I'm an ass, I didn't even test it in the interpreter. 
> > Please
> > find attached a revised patch.


> > felix

> Dear felix,

> the latest patch works. I extended my test code and here are the results:

> without -C -mfma:

> csc -O5 -d0 -C -O3 fma-test.scm && ./fma-test
> 7.998s CPU time, 0/225861 GCs (major/minor), maximum live heap: 30.78 MiB
> 10.104s CPU time, 0/256410 GCs (major/minor), maximum live heap: 30.78 MiB
> 10.69s CPU time, 0/311364 GCs (major/minor), maximum live heap: 30.78 MiB

> with -C -mfma:

> csc -O5 -d0 -C -O3 -C -mfma fma-test.scm && ./fma-test
> 7.697s CPU time, 0/238095 GCs (major/minor), maximum live heap: 30.78 MiB
> 9.135s CPU time, 0/262467 GCs (major/minor), maximum live heap: 30.78 MiB
> 11.008s CPU time, 0/317460 GCs (major/minor), maximum live heap: 30.78 MiB

> It seems the number of GCs is a lot higher than for fp*/fp+ or c99-fma with 
> or without fma compiler flag. So currently, there seems to be no benefit 
> integrating c99's fma as fp*+ besides a slightly better rounding error. At 
> least for me, this comes unexpected.

> Thank you for providing the patch. If you want to test something in this 
> regard in the future, I am happy to test further patches.

> Cheers

> Christian

Dear felix,

after coming back to this function and the associated issues regularly, I 
revised my opinion on integrating"fp+*" into (chicken flonum), given it uses 
the C99-fma function. On the one hand, this operation is so fundamental in 
numerical computations that it warrants a specialized function, on the other 
hand the (somewhat) improved rounding could help a little. Finally, Gauche ( 
https://practical-scheme.net/gauche/man/gauche-refe/R7RS-large.html#index-fl_002b_002a
 ) and MIT Scheme ( 
https://www.gnu.org/software/mit-scheme/documentation/stable/mit-scheme-ref.html#Flonum-Operations
 ) provide this functionality. All in all, I would really appreciate if an 
inclusion of a fma-based "fp+*" function into the (chicken flonum) module could 
be considered in future versions of CHICKEN Scheme. Maybe your provided patch 
reduces the effort for this.

Thank you very much

Christian