https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65641
--- Comment #2 from Jens Breitbart <j.breitbart at tum dot de> --- Thanks for the link. I am not sure if there is really any benefit of using libdivide instead of the masking. I'll attach a first version of patch in which the functor stores the mask. Any comments welcome, I am not familiar with the library. Another possible solution would be to allow the number of buckets to be a power of two, as one can easily compute the mask for such cases. This could be triggered by the user explicitly calling rehash() with a power of two as the parameter. Increasing the number of buckets would only increase to another power of two. _Mod_range_hashing could check if the number of buckets is a power of two and use masking in that case. This would not require an ABI change. Any chance of getting such a change upstream? As far as I can see, there seems to be no easy way to have the unorered_map use our folding functor instead of _Mod_range_hashing or am I missing something?
