From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Eli Zaretskii Newsgroups: gmane.emacs.bugs Subject: bug#32605: [w64] (random) never returns negative Date: Fri, 13 Aug 2021 09:29:41 +0300 Message-ID: <83czqhdfhm.fsf@gnu.org> 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> Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="18346"; mail-complaints-to="usenet@ciao.gmane.io" Cc: 32605@debbugs.gnu.org To: Andy Moreton Original-X-From: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane-mx.org@gnu.org Fri Aug 13 08:31:32 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 1mEQj5-0004cb-C1 for geb-bug-gnu-emacs@m.gmane-mx.org; Fri, 13 Aug 2021 08:31:31 +0200 Original-Received: from localhost ([::1]:47220 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mEQj4-0007n2-3g for geb-bug-gnu-emacs@m.gmane-mx.org; Fri, 13 Aug 2021 02:31:30 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:33050) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mEQic-0007mp-Ro for bug-gnu-emacs@gnu.org; Fri, 13 Aug 2021 02:31:03 -0400 Original-Received: from debbugs.gnu.org ([209.51.188.43]:57082) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1mEQic-0002az-KR for bug-gnu-emacs@gnu.org; Fri, 13 Aug 2021 02:31:02 -0400 Original-Received: from Debian-debbugs by debbugs.gnu.org with local (Exim 4.84_2) (envelope-from ) id 1mEQic-0006y7-6b for bug-gnu-emacs@gnu.org; Fri, 13 Aug 2021 02:31:02 -0400 X-Loop: help-debbugs@gnu.org Resent-From: Eli Zaretskii Original-Sender: "Debbugs-submit" Resent-CC: bug-gnu-emacs@gnu.org Resent-Date: Fri, 13 Aug 2021 06:31:02 +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 Original-Received: via spool by 32605-submit@debbugs.gnu.org id=B32605.162883620226650 (code B ref 32605); Fri, 13 Aug 2021 06:31:02 +0000 Original-Received: (at 32605) by debbugs.gnu.org; 13 Aug 2021 06:30:02 +0000 Original-Received: from localhost ([127.0.0.1]:40395 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from ) id 1mEQhe-0006vX-6F for submit@debbugs.gnu.org; Fri, 13 Aug 2021 02:30:02 -0400 Original-Received: from eggs.gnu.org ([209.51.188.92]:44610) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from ) id 1mEQhb-0006up-Ot for 32605@debbugs.gnu.org; Fri, 13 Aug 2021 02:30:00 -0400 Original-Received: from fencepost.gnu.org ([2001:470:142:3::e]:36880) by eggs.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mEQhW-0001WY-EU; Fri, 13 Aug 2021 02:29:54 -0400 Original-Received: from 84.94.185.95.cable.012.net.il ([84.94.185.95]:3096 helo=home-c4e4a596f7) by fencepost.gnu.org with esmtpsa (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mEQhW-0002hK-0B; Fri, 13 Aug 2021 02:29:54 -0400 In-Reply-To: <86bl62s8qm.fsf@gmail.com> (message from Andy Moreton on Thu, 12 Aug 2021 21:34:09 +0100) 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:211715 Archived-At: > From: Andy Moreton > Date: Thu, 12 Aug 2021 21:34:09 +0100 > > > int val = ((rand_as183 () << 15) | rand_as183 ()); > > #ifdef __x86_64__ > > return 2 * val - 0x3FFFFFFF; > > #else > > return val; > > #endif > > > > Andy, can you test this, please? > > That does not produce any negative random numbers within a reasonable > number of attempts (a few dozen calls). Thanks for testing. > Instead, calling rand_as183 again (as below) does produce positive and > negative random numbers on 32bit and 64bit builds with a similar number > of attempts: > > return ((rand_as183 () << 30) | (rand_as183 () << 15) | rand_as183 ()); > > While this may be less efficient, it at least meets the contract of > providing 31 random bits. What about the variant below, does it produce better results? int val = ((rand_as183 () << 15) | rand_as183 ()); #ifdef __x86_64__ return 2 * val - 0x7FFFFFFF; #else return val; #endif