Re: Interesting performance quirk.

["Peter C. Chapin" <pcc482719@gmail.com>]

Florian Weimer wrote:

> Is memory allocation or finalization involved in an inner loop?
> It might also help to compare -gnatdg output or assembly (-S).

No, the inner loop is pretty much plain computation. The array over
which I work is dynamically allocated, however. So I suppose the Ada
version is doing checks to make sure the access value that points at the
array isn't null, whereas the C version is probably not doing that. I'm
not sure how much of an effect those null checks would have, though.
Blowfish's uses 16 "rounds" on each block so depending on where the
checks are done they could be lost in the overhead of the algorithm...
or not.

As Martin said in another post, I understand that by making some
adjustments to the code one can often coax the compiler to skip checks
that are actually unnecessary without violating the semantics of Ada. I
will definitely have to look into that. Thanks for your suggests above
for getting further information. I would definitely like to understand
*why* the code is slow before spending too much time try to fix it. I've
optimized code before (not Ada code) and I know that just guessing about
the problem often doesn't work well.

Peter