Re: [boost] [hash] regular behaviour of hash function for double values

Subject: Re: [boost] [hash] regular behaviour of hash function for double values
From: Dave Abrahams (dave_at_[hidden])
Date: 2012-01-31 11:19:29

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_at_[hidden]> 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.

-- 
Dave Abrahams
BoostPro Computing
http://www.boostpro.com