public inbox for gcc-bugs@sourceware.org help / color / mirror / Atom feed
From: "redi at gcc dot gnu.org" <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 12:56:00 -0000 [thread overview] Message-ID: <bug-65641-4-XzisAKrlyM@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 Jonathan Wakely <redi at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |NEW Last reconfirmed| |2015-04-02 CC| |fdumont at gcc dot gnu.org Ever confirmed|0 |1 Severity|normal |enhancement --- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> --- (In reply to Jens Breitbart from comment #2) > 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. That sounds promising, and worth pursuing. > Any chance of getting such a change upstream? I don't see why not, although unless you have a GCC copyright assignment on file, or plan to get one (immediately, since it can take a while) it's better *not* to give us a patch, because we can't use it anyway and there can be no danger of using your code if we don't see it! > 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? I think you would need to use the _Hastable class template directly, rather than via std::unordered_map. In theory that allows you to re-use the internals with different policies, but in practice it's not very easy.
next prev parent reply other threads:[~2015-04-02 12:56 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 2015-04-02 12:56 ` redi at gcc dot gnu.org [this message] 2015-05-02 18:35 ` glisse at gcc dot gnu.org
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=bug-65641-4-XzisAKrlyM@http.gcc.gnu.org/bugzilla/ \ --to=gcc-bugzilla@gcc.gnu.org \ --cc=gcc-bugs@gcc.gnu.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).