[darcs-users] darcs patch: remove quadratic blowups from mapPrimFL

[David Roundy]

On Thu, Oct 30, 2008 at 06:01:26AM +0000, Ganesh Sittampalam wrote:
> On Wed, 29 Oct 2008, Jason Dagit wrote:
> >Have you retimed things with the full set of patches you submitted?
> >Do you know what the overall improvement would be?
> 
> Nope - without some really good "fire and forget" infrastructure and a
> dedicated machine that can be guaranteed quiescent, benchmarking is quite 
> fiddly and time-consuming, so I've only been doing it for things where it 
> seemed particularly warranted.

I've just reviewed this one, and it looks correct, but I couldn't predict
whether its performance behavior.  So I'd rather not apply it, unless
either you can explain it to me in such a way that I can understand the
improvement is, or you have benchmarks demonstrating the improvement.

I can see that you replace (+>+) with (:>:) using some clever tricks (which
is definitely always a bonus), but that only affects the scaling when many,
many changes are made to a single file, in which case this is almost
certainly not a bottleneck (since we're diffing said file, which is a slow
operation).

The other change (and I think these two changes are separable?) is a switch
from foldl' to foldr, and I must admit that these fold functions almost
always confuse the heck out of me...
-- 
David Roundy
http://www.darcs.net