On Nov 17, 2010, at 4:06 PM, Jed Brown wrote:
> On Wed, Nov 17, 2010 at 22:41, Barry Smith <bsmith at mcs.anl.gov> wrote:
> I hate beyond words the standard C++ template model
>
> Me too.
>
> This, I think, can be done using ONLY simple C++ function polymorphism
> (allowing VecSetValues(double*) and VecSetValues(single *) for example)
>
> If I call VecGetArray(X,&singleptr) and X is "double", would this error or
> make a copy?
In Model II it is an error (runtime) whenever you call an object of one
precision with a function that exposes a different precision.
> What about "local" callbacks (or any callback that passes scalars)? And any
> composed function (that part is not type safe, so C++ name mangling won't
> save you)?
Beats me.
>
> An acceptable C solution might be to have a PetscShortScalar typedef,
> VecGetArrayShort(), and maybe also MatSetValuesShort() (integration for
> assembly can be time consuming, and float is twice as fast if you vectorize
> well) which would give you no-copy access to short storage. You could still
> have C++ overloaded variants, but I usually want some explicit control over
> types matching. To allow people to make their Shorts (likely float) into
> Longs (likely double), have them recompile with a macro defined that causes
> the Short names to be defined to the long ones.
Yuck :-). This doesn't really simplify things anyways because there are
billions of places where calls are made where the calling function has a
exposed precision in one of the arguments. Somehow you've got to get PETSc
compiled with both precisions and in the same library.
>
> But this does snowball if you want {Real,Complex}{Short,Long} in the same
> code.
>
> Documentation for the Short variants could be organized so that it doesn't
> cause clutter, but hopefully there aren't a huge number that need this
> specialization.
>
>
> Thanks for the summary, I hope it works out.
After a tiny bit of hard earned success I'm thinking redoing all of PETSc
with proper code generation :-) What will I think tommorow :-(
Barry
>
> Jed
