[ODE] Sweep-and-Prune space for ODE

Graham Fyffe gfyffe at gmail.com
Fri Nov 26 11:00:20 MST 2004

Yes, I did modify all the algorithms I tested to have the same
interface and operate on the same data.  I also tried with and without
prefetching on the radix sort, and even without it it's very fast.  I
didn't get them to produce ranks, however.

To solve that, I could 1) sort arbitrary objects based on a key, like
std::sort does, or I could 2) produce a list of ranks instead of
sorting the data.  Which one does ODE need?  It would be pretty easy
to change the interface to the sort routines.

- Graham

On Fri, 26 Nov 2004 16:10:25 +0100, Pierre Terdiman
<pierre.terdiman at novodex.com> wrote:
> > Okay, now THAT is a nice implementation of radix sort.  For floats, it
> > is 2.3 times faster than std::sort!  That means it's 5 times faster
> > than Pierre's code.  Five.  I would strongly suggest that anyone using
> > Pierre's code should switch to the stereopsis code.
> BTW, if you really want relevant numbers you should make sure all versions
> do the same things. For example the memory buffers for the radix sort are
> allocated outside the sort routine in Michael's code snippet, while it's
> done within the RadixSort class in mine (that is, it's usually profiled
> too!). Allocating memory for 50,000,000 elements might take some significant
> time, for example.
> The prefetch instructions is another thing you might want to consider. As
> far as I'm concerned, I didn't want to use them in sake of compatibility
> with non-SSE machines (at the time, I didn't even have one). So, *of course*
> taking advantage of this gives the 25% speedup Michael mentions. But there's
> a price to pay for this.
> Over the years, I've been sent quite a few "faster" sort routines by
> different people. The most common mistake is the problem I already mentioned
> : not providing ranks as output. This is quite a significant speed boost !
> Adding ranks immediately makes you touch twice as much memory, and it's
> often enough to double the CPU time as well.
> Overall I found that radix sort to be quite ok, often faster than the
> alternatives.
> - Pierre

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