On Tuesday, January 31, 2012 11:19:29 Dave Abrahams wrote:
on Tue Jan 31 2012, Olaf van der Spek <ml-AT-vdspek.org> wrote:
On Tue, Jan 31, 2012 at 4:10 PM, Kai Schroeder
<kaischroeder3@googlemail.com> wrote:
Especially since some hash table implementations (e.g. intel's threading building blocks) only use the last few bits to determine the bucket, this can lead to very bad caching behaviour for the rather common case of regularly sampled points (equidistant samplings of power of 2 are e.g. common in computer graphics and numerical algorithms).
Are you aware of this? Would you consider it a bug?
Yes, sounds like a bug in TBB. I don't think it's a good idea to discard bits.
Perhaps not, but it seems to me that we have a problem, too.
In case you missed it, there was this [1] conversation which basically boiled down to where bit mixing of the hash value should be implemented - in the hash function or the container itself. The standard doesn't mandate this, AFAICT, but my understanding is that it's the hash function's job. [1] <http://news.gmane.org/find- root.php?group=gmane.comp.lib.boost.devel&article=227609>