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 13:10:08 +0100 Message-ID: <86fsvcz0pr.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> <86sfzcjnfr.fsf@gmail.com> <835yw8b6s3.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="17931"; 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:XDr7l4Sjj0jCkBmjtmGR6cKxMcI= Original-X-From: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane-mx.org@gnu.org Sat Aug 14 14:11:58 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 1mEsW6-0004Rp-Cu for geb-bug-gnu-emacs@m.gmane-mx.org; 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Sat, 14 Aug 2021 14:10:16 +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:211827 Archived-At: On Sat 14 Aug 2021, Eli Zaretskii wrote: >> From: Andy Moreton >> Date: Sat, 14 Aug 2021 12:06:00 +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': > > Why not keep the 30 bits we produce today on 32-bit builds? For 32bit builds (FIXNUM_BITS is 30), either: a) define RAND_BITS to 30, 'random' calls 'rand_as183' twice. 'get_random' needs 1 call to 'random' (total 2 calls of 'rand_as183'). b) define RAND_BITS to 15, 'random' calls 'rand_as183' once. 'get_random' needs 2 calls to 'random' (total 2 calls of 'rand_as183'). For 64bit builds (FIXNUM_BITS is 62), either: a) define RAND_BITS to 30, 'random' calls 'rand_as183' twice. 'get_random' needs 3 calls to 'random' (total 6 calls of 'rand_as183'). b) define RAND_BITS to 15, 'random' calls 'rand_as183' once. 'get_random' needs 4 calls to 'random' (total 4 calls of 'rand_as183'). On 32bit builds both options are roughly equivalent. On 64bit builds option (b) is better as option (a) does unnecessary work. AndyM