On 31 January 2012 20:31, Christopher Jefferson <chris@bubblescope.net> wrote:
On 31 Jan 2012, at 19:58, Daniel James wrote:
On 31 January 2012 16:19, Kai Schroeder <kaischroeder3@googlemail.com> wrote:
Well, I tend to agree that this is a bug in TBB
I actually don't. If TBB requires a better quality hash function, then that's fine. I also wouldn't use boost::hash or std::hash with google's hash tables.
It would be easy to provide a boost::hash_shuffle, that could be applied to any boost::hash and provide this stronger requirement (that there is no corrolation between (a-b) and (hash(a)-hash(b)). This would avoid the need to re-write all the existing hash functions.
Feel free to do so. Although, I'd probably write it to use better algorithms where possible, and just use boost::hash as a fallback for when they're not. I think I've mentioned before that I regret calling it 'boost::hash', 'boost::functional::hash' would have been a better name. Btw. to go back to the original post, I might change the mix function for floats, it might be problematic as it is. Also, the float hash is actually a bit slow because it's doesn't rely on the binary representation of floating point numbers. But when the binary representation is known to be safely hashable, it might be better to hash that. I already do that for cygwin because the floating point functions weren't available there. The problem is accounting for the different representations, which I don't want to spend too much time dealing with.