From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Andy Moreton Newsgroups: gmane.emacs.bugs Subject: bug#32605: [w64] (random) never returns negative Date: Sat, 14 Aug 2021 12:06:00 +0100 Message-ID: <86sfzcjnfr.fsf@gmail.com> References: <855zzpf86u.fsf@gmail.com> <87zhx1ktp0.fsf@gmx.net> <87zhwwhp9i.fsf@gmail.com> <87mtpmls3p.fsf_-_@gnus.org> <83o8a2dbjo.fsf@gnu.org> <86bl62s8qm.fsf@gmail.com> <83czqhdfhm.fsf@gnu.org> <861r6xoxqa.fsf@gmail.com> <83sfzcbmfm.fsf@gnu.org> <86mtpksa0l.fsf@gmail.com> <83a6lkbe02.fsf@gnu.org> Mime-Version: 1.0 Content-Type: text/plain Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="3411"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (windows-nt) To: 32605@debbugs.gnu.org Cancel-Lock: sha1:Xa01Ld8fj+zt1+qoI2gRqfO2oA4= Original-X-From: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane-mx.org@gnu.org Sat Aug 14 13:07:13 2021 Return-path: Envelope-to: geb-bug-gnu-emacs@m.gmane-mx.org Original-Received: from lists.gnu.org ([209.51.188.17]) by ciao.gmane.io with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1mErVQ-0000eM-HU for geb-bug-gnu-emacs@m.gmane-mx.org; Sat, 14 Aug 2021 13:07:12 +0200 Original-Received: from localhost ([::1]:55846 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mErVO-0002Dz-Rr for geb-bug-gnu-emacs@m.gmane-mx.org; Sat, 14 Aug 2021 07:07:10 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:46784) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mErVI-0002Cn-Gs for bug-gnu-emacs@gnu.org; Sat, 14 Aug 2021 07:07:04 -0400 Original-Received: from debbugs.gnu.org ([209.51.188.43]:60348) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1mErVG-0007Fa-6t for bug-gnu-emacs@gnu.org; Sat, 14 Aug 2021 07:07:03 -0400 Original-Received: from Debian-debbugs by debbugs.gnu.org with local (Exim 4.84_2) (envelope-from ) id 1mErVF-0005fo-UY for bug-gnu-emacs@gnu.org; Sat, 14 Aug 2021 07:07:01 -0400 X-Loop: help-debbugs@gnu.org In-Reply-To: <855zzpf86u.fsf@gmail.com> Resent-From: Andy Moreton Original-Sender: "Debbugs-submit" Resent-CC: bug-gnu-emacs@gnu.org Resent-Date: Sat, 14 Aug 2021 11:07:01 +0000 Resent-Message-ID: Resent-Sender: help-debbugs@gnu.org X-GNU-PR-Message: followup 32605 X-GNU-PR-Package: emacs X-GNU-PR-Keywords: confirmed X-Debbugs-Original-To: bug-gnu-emacs@gnu.org Original-Received: via spool by submit@debbugs.gnu.org id=B.162893917921743 (code B ref -1); Sat, 14 Aug 2021 11:07:01 +0000 Original-Received: (at submit) by debbugs.gnu.org; 14 Aug 2021 11:06:19 +0000 Original-Received: from localhost ([127.0.0.1]:43661 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from ) id 1mErUZ-0005ed-5i for submit@debbugs.gnu.org; Sat, 14 Aug 2021 07:06:19 -0400 Original-Received: from lists.gnu.org ([209.51.188.17]:43336) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from ) id 1mErUW-0005eV-TZ for submit@debbugs.gnu.org; Sat, 14 Aug 2021 07:06:17 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:46754) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mErUW-00020W-OD for bug-gnu-emacs@gnu.org; Sat, 14 Aug 2021 07:06:16 -0400 Original-Received: from ciao.gmane.io ([116.202.254.214]:50776) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mErUS-0006Yf-1V for bug-gnu-emacs@gnu.org; Sat, 14 Aug 2021 07:06:13 -0400 Original-Received: from list by ciao.gmane.io with local (Exim 4.92) (envelope-from ) id 1mErUP-0009ts-NW for bug-gnu-emacs@gnu.org; Sat, 14 Aug 2021 13:06:09 +0200 X-Injected-Via-Gmane: http://gmane.org/ Received-SPF: pass client-ip=116.202.254.214; envelope-from=geb-bug-gnu-emacs@m.gmane-mx.org; helo=ciao.gmane.io X-Spam_score_int: 5 X-Spam_score: 0.5 X-Spam_bar: / X-Spam_report: (0.5 / 5.0 requ) BAYES_00=-1.9, DKIM_ADSP_CUSTOM_MED=0.001, FORGED_GMAIL_RCVD=1, FREEMAIL_FORGED_FROMDOMAIN=0.249, FREEMAIL_FROM=0.001, HEADER_FROM_DIFFERENT_DOMAINS=0.25, NML_ADSP_CUSTOM_MED=0.9, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: debbugs-submit@debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list X-BeenThere: bug-gnu-emacs@gnu.org List-Id: "Bug reports for GNU Emacs, the Swiss army knife of text editors" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane-mx.org@gnu.org Original-Sender: "bug-gnu-emacs" Xref: news.gmane.io gmane.emacs.bugs:211819 Archived-At: On Sat 14 Aug 2021, Eli Zaretskii wrote: >> From: Andy Moreton >> Date: Sat, 14 Aug 2021 09:31:06 +0100 >> >> I'm not an expert on random numbers either, and your efforts are not an >> annoyance, but I am puzzled why you so strongly prize performance over >> correctness in this instance. > > Because I have no idea how important the "correctness" part is, or > why. OTOH, this stuff, when used, tends to be in the inner loops, so > performance matters. I doubt anyone expects cryptographic quality randomness or any given statistical distribution from such a general purpose routine, but they have a reasonable expectation that the results from 'get_random' do not have stuck bits that are always non-random. In which case perhaps the solution is to change the RAND_BITS logic in sysdep.c on Windows to override the RAND_BITS definition: + #ifdef WINDOWSNT + /* Use w32.c replacement for random(). */ + # define RAND_BITS 15 + #endif #ifndef RAND_BITS # ifdef HAVE_RANDOM # define RAND_BITS 31 # else /* !HAVE_RANDOM */ ... #endif ..and then in w32.c make 'random' return the 15bit value from 'rand_as183': int random (void) { /* rand_as183 () gives us 15 random bits. */ return rand_as183 (); } That should result in 'get_random' receiving 15 bits of randomness in each loop iteration and thus computing a valid result. [This could obviously be optimised to open code 'rand_as183' in 'random', or allow the compiler to inline it by moving the w32.c implementations of 'random' and 'srandom' into sysdep.c] As 'get_random_bignum' (in fns.c) calls 'get_random' in a loop, that should also remove bugs from that function on this platform. Perhaps this would be helped by having a test for 'get_random', to check that every bit of a fixnum is toggled after a reasonable number of calls. While that does not test the statistical distribution of the random number sequence, it would ensure that the values returned by 'get_random' are not always positive, or always even, etc. AndyM