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From: "j.breitbart at tum dot de" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug libstdc++/65641] unordered_map - __detail::_Mod_range_hashing is slow Date: Thu, 02 Apr 2015 12:37:00 -0000 [thread overview] Message-ID: <bug-65641-4-IYq1Tl10GN@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-65641-4@http.gcc.gnu.org/bugzilla/> 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?
next prev parent reply other threads:[~2015-04-02 12:37 UTC|newest] Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top 2015-03-31 14:20 [Bug libstdc++/65641] New: " j.breitbart at tum dot de 2015-03-31 17:29 ` [Bug libstdc++/65641] " redi at gcc dot gnu.org 2015-04-02 12:37 ` j.breitbart at tum dot de [this message] 2015-04-02 12:56 ` redi at gcc dot gnu.org 2015-05-02 18:35 ` glisse at gcc dot gnu.org
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