On Wed, 16 Oct 2013 22:16:09 +0100, Ted Dunning wrote:
Does this really add comparisons on average? Or does it only add
comparisons on key equality? If the latter the difference is
definitely
minute.
In the particular case ("MathArrays.sortInPlace") the current
comparator
only compares keys; the new comparator adds an "if" for each such
comparison.
Hmm, I now wonder whether it is at all correct to add the comparison of
values
in that case (and I start to wonder why the tests still pass).
Secondly, changing comparator value to include value changes how sets
work.
Usually, this is good. Occasionally bad. In any case, a change
that is
rather subtle and difficult to determine whether there is an impact.
OK, so better not rush with this change...
Gilles
On Wed, Oct 16, 2013 at 10:10 PM, Sean Owen <sro...@gmail.com> wrote:
You are right that it adds 1 or 2 more branches per comparison. The
new
Comparator would at least be consistent with equals(), though it
probably
doesn't matter for correctness in practice.
I am interested in closing this minor issue so I suggest you ignore
this
part if you guess that this overhead is too much, and that it's not
worth
offering this for other callers of CM. I'll just maintain my own
copy.
On Wed, Oct 16, 2013 at 9:56 PM, Gilles
<gil...@harfang.homelinux.org
>wrote:
>
>
> The potential problem is performance. The current code for
"sortInPlace"
is
> not as fast as it could be, very probably because it uses a
Comparator.
> IIUC,
> using your new comparator will add another "if" (to test whether
comparing
> the
> "value"s is necessary). [And "reverseOrder" will also add a few
operations
> on
> its own, I guess.]
> It would be nice to know whether the impact is really fairly
negligible,
or
> not.
>
> There is a class (in the "test" part of repository) for performing
simple
> benchmarks:
> org.apache.commons.math3.**PerfTestUtils
> that tries to provide fair comparison results by interleaving
calls to
two
> (or more) alternative codes.
>
>
> Best regards,
>
> Gilles
>
>
>
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