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

Subject: Re: [boost] [hash] regular behaviour of hash function for double values
From: Stephan T. Lavavej (stl_at_[hidden])
Date: 2012-01-31 12:59:36

[Kai Schroeder]
> I have found that this behaviour of boost hash is described in the
> documentation:
> http://www.boost.org/doc/libs/1_48_0/doc/html/hash/rationale.html

> So, this is by design. This rationale is understandable, however it
> can lead to difficult to find performance problems as in our case.
> Btw.: std::hash in MSVC10 does not show this behaviour. Well, I tend
> to agree that this is a bug in TBB, still I would personally prefer a
> better hash function (even if it is a bit slower) by default. Maybe a
> fast_hash option could be provided as an alternative.

In VC11, we've reimplemented std::hash. We now use FNV-1a for everything, which is incredibly fast (significantly faster than before, according to my measurements) and pretty good at mixing bits.

STL