Hi, On Thu, 10 Sep 2015, François Dumont wrote:
> Here is a patch to offer an alternative hash policy. This one is > using power of 2 number of buckets allowing a faster modulo operation. > This is obvious when running the performance test that I have adapted to > use this alternative policy. Something between current implementation > and the tr1 one, the old std one. > > Of course with this hash policy the lower bits of the hash code are > more important. For pointers it would require to change the std::hash > implementation to remove the lower 0 bits like in the patch I proposed > some weeks ago. > > What do you think ? No comment on if it should be included (except that it seems useful to me), but one observation of the patch: > + 1ul << 31, > +#if __SIZEOF_LONG__ != 8 > + 1ul << 32 > +#else This is wrong, 1ul<<32 is zero on a 32bit machine, and is also the 33rd entry in that table, when you want only 32. Like you also (correctly) stop with 1ul<<63 for a 64bit machine. Ciao, Michael.
