On Tuesday, 11 June 2013 at 21:26:35 UTC, John Colvin wrote:
On Tuesday, 11 June 2013 at 20:46:32 UTC, Craig Dillabaugh
wrote:
I was looking at D code for constructing kd-trees, the full
code
listing for which can be found here:
clip
So my question is, does anyone have any idea why the author may
have used templates here. It was on Rosettacode so maybe they
are
just there to show off D's nice template abilities, but I am
curious if in idiomatic D using templates this way is somehow
superior to the function parameter method I would have tried.
Cheers,
Craig
It's just a trade-off between template bloat and having more
values hard-coded in for efficiency.
In this particular case, due to the use of the static array in
KdNode, if idx is known at compile time then the optimizer can
go to town on those loops in findMedian. e.g. in
foreach (p; start .. end) {
if (p.x[idx] < pivot) {
if (p != store)
swap(p.x, store.x);
store++;
}
}
given offset = p.x.offsetof + idx
p.x[idx] becomes just *(p+offset) which is fast and completely
predictable behaviour. Great for optimizers and cache
prefetching etc...
All that is meaningless guesswork though, the only thing that
will tell you for sure is benchmarking and profiling.
Thanks. This makes sense. If I can find the time perhaps I will
run some benchmarks on it.
