From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED!not-for-mail From: Stefan Monnier Newsgroups: gmane.emacs.devel Subject: Re: Making 'eq' == 'eql' in bignum branch Date: Sun, 19 Aug 2018 20:04:35 -0400 Message-ID: References: <29f933ac-a6bf-8742-66a7-0a9d6d3e5a88@disroot.org> <0d3175d8-d996-651e-b221-71978bde3a65@cs.ucla.edu> <87tvpdnzgy.fsf@tromey.com> <4c2a814f-c254-29e5-39cf-11b5f2e5c9c8@cs.ucla.edu> <49d8ba62-c9a5-9203-d882-8e900b441ff3@cs.ucla.edu> <8e0320d9-e0d0-2b57-57cc-2df4399f133c@cs.ucla.edu> <87lgaio7xd.fsf@tromey.com> <877em1cb0i.fsf@tromey.com> <765767b2-d2e5-a9a6-f724-d58ecf4847bb@cs.ucla.edu> <76081b5d-8c10-0a37-2c97-d4864c0faa80@cs.ucla.edu> <09153aed-361d-4f82-d9ac-b502314769ae@cs.ucla.edu> NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain X-Trace: blaine.gmane.org 1534723376 21080 195.159.176.226 (20 Aug 2018 00:02:56 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Mon, 20 Aug 2018 00:02:56 +0000 (UTC) User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.0.50 (gnu/linux) Cc: emacs-devel@gnu.org To: Paul Eggert Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Mon Aug 20 02:02:51 2018 Return-path: Envelope-to: ged-emacs-devel@m.gmane.org Original-Received: from lists.gnu.org ([208.118.235.17]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1frXel-0005NY-1L for ged-emacs-devel@m.gmane.org; Mon, 20 Aug 2018 02:02:51 +0200 Original-Received: from localhost ([::1]:44500 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1frXgr-00006A-Dc for ged-emacs-devel@m.gmane.org; Sun, 19 Aug 2018 20:05:01 -0400 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:55500) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1frXgk-00005m-TM for emacs-devel@gnu.org; Sun, 19 Aug 2018 20:04:55 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1frXgh-0003qn-GY for emacs-devel@gnu.org; Sun, 19 Aug 2018 20:04:54 -0400 Original-Received: from chene.dit.umontreal.ca ([132.204.246.20]:43543) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1frXgh-0003q3-9a for emacs-devel@gnu.org; Sun, 19 Aug 2018 20:04:51 -0400 Original-Received: from fmsmemgm.homelinux.net (lechon.iro.umontreal.ca [132.204.27.242]) by chene.dit.umontreal.ca (8.14.7/8.14.1) with ESMTP id w7K04ZUT027824; Sun, 19 Aug 2018 20:04:37 -0400 Original-Received: by fmsmemgm.homelinux.net (Postfix, from userid 20848) id 15EB2AE1F5; Sun, 19 Aug 2018 20:04:35 -0400 (EDT) In-Reply-To: <09153aed-361d-4f82-d9ac-b502314769ae@cs.ucla.edu> (Paul Eggert's message of "Sat, 28 Jul 2018 20:34:32 -0700") X-NAI-Spam-Flag: NO X-NAI-Spam-Threshold: 5 X-NAI-Spam-Score: 0 X-NAI-Spam-Rules: 2 Rules triggered EDT_SA_DN_PASS=0, RV6354=0 X-NAI-Spam-Version: 2.3.0.9418 : core <6354> : inlines <6821> : streams <1795990> : uri <2691987> X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 132.204.246.20 X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: "Emacs development discussions." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Original-Sender: "Emacs-devel" Xref: news.gmane.org gmane.emacs.devel:228702 Archived-At: Regarding `eq` for bignums, there seems to be some reluctance to just defining `eq` to be an alias of the current `eql` and I think I agree because my current approach is more costly now with the new bignum code: `eql` used to just do FLOATP (x) ? costly_eql (x, y) : EQ (x, y) where FLOATP would just check the 3 low bits of `x`. But now we have to do (FLOATP (x) || BIGNUMP (x)) ? costly_eql (x, y) : EQ (x, y) where BIGNUMP not only checks the low order bits of `x` but also looks at the pseudovector_header of `x` if x is a pseudovector (to see if it's a bignum), so the cost in CPU time is larger and the cost in code size is even larger yet. So I think hash-consing bignums makes sense. It will bring us back the equivalence between `eq` and `eql` for integers (hence bringing us closer to making `eq == eql` which I think is a very worthy goal), and I think its cost should not be too high in practice: the time to lookup up a GMP number in a hash table basically should never be longer than the time it took to construct this number in the first place, so that's a worst-case slowdown factor of 2 which I think is perfectly acceptable. Stefan