From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from joooj.vinc17.net (joooj.vinc17.net [155.133.131.76]) by sourceware.org (Postfix) with ESMTPS id E0C133858298 for ; Fri, 16 Feb 2024 12:39:51 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org E0C133858298 Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=vinc17.net Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=vinc17.net ARC-Filter: OpenARC Filter v1.0.0 sourceware.org E0C133858298 Authentication-Results: server2.sourceware.org; arc=none smtp.remote-ip=155.133.131.76 ARC-Seal: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1708087193; cv=none; b=cVLrdypa2JvtxSs6ENf/EjLNchrhkDUrbHjCOpYvNvoROSISgCx2KqG7uOsfUQf13MnbsVF+nMq9CYY91Gzsknf0FClcmnCacpLh/m/6BRb65xx95rvSj2Ep437k3GN5WvGS6JClVePg003dNN5gaMCI/PgB7NK5YG8hEZpZ/kI= ARC-Message-Signature: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1708087193; c=relaxed/simple; bh=udG8w0KnDKO9lp7cL5F6pCVo+ufUAgWcQ5lLcjoq1co=; h=Date:From:To:Subject:Message-ID:MIME-Version; b=hKQ+YT1hIs514m9I2ekAVGifO412n56jybQBo3zxTDnwYlnnuKAFqizA/Ql/9Ub9n1BLz+mEvwIFZpp4czEr5Fi+QJP1vKo4Vr7WNMHjAX/P7CuoY8FyIMdkZ6vFWnQ957j5aeXK7sKi9HCeZGHS07vJaW89DMyQb/ZOrNP5xG4= ARC-Authentication-Results: i=1; server2.sourceware.org Received: from smtp-qaa.vinc17.net (2a02-8428-1b1d-4d01-96a9-491d-7b48-ba31.rev.sfr.net [IPv6:2a02:8428:1b1d:4d01:96a9:491d:7b48:ba31]) by joooj.vinc17.net (Postfix) with ESMTPSA id DA1183DA; Fri, 16 Feb 2024 13:39:50 +0100 (CET) Received: by qaa.vinc17.org (Postfix, from userid 1000) id A4BF1CA3236; Fri, 16 Feb 2024 13:39:50 +0100 (CET) Date: Fri, 16 Feb 2024 13:39:50 +0100 From: Vincent Lefevre To: libc-alpha@sourceware.org Subject: Re: document the fact that "Known Maximum Errors" might not be maximal Message-ID: <20240216123950.GC3653@qaa.vinc17.org> Mail-Followup-To: Vincent Lefevre , libc-alpha@sourceware.org References: <20240216094334.GA3653@qaa.vinc17.org> <20240216102258.GB3653@qaa.vinc17.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Mailer-Info: https://www.vinc17.net/mutt/ User-Agent: Mutt/2.2.12+69 (354c5b11) vl-149028 (2023-12-10) X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,KAM_DMARC_STATUS,SPF_HELO_NONE,SPF_PASS,TXREP,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: On 2024-02-16 11:54:03 +0100, Paul Zimmermann wrote: > Vincent, > > > If I understand correctly, Carlos means (unintended) bugs, in which > > case, values may even be completely wrong (as already seen). I think > > that saying "documented elsewhere" is misleading. And note that bugs > > are not specific to the math functions. Any buggy library function > > will not behave as described in the manual. You should rather say > > that the given bounds obviously do not take bugs into account, if > > you think that this is worth recalling. > > of course *unknown* bugs might exist, but we are speaking of *known* > defects here. Well, known bugs in non-math functions are never documented either. For instance, concerning regexps, there is bug 10844[*], which has been known since 2009 (more than 14 years ago) and is not documented. [*] https://sourceware.org/bugzilla/show_bug.cgi?id=10844 > The issue is that the manual says "*Known* Maximum Errors in Math Functions". > > What do you suggest to avoid users deducing from the manual that the ulp error on say y0 > is bounded by 3 ulps on x86_64, whereas it can be as large as 5.93e15 ulps? > > Checking y0 with glibc-2.39/build and rndn > GNU libc version: 2.39 > GNU libc release: stable > y0 0 -1 0x1.c982eb8d417eap-1 [5920543797734652] [5.93e+15] 5.92055e+15 5920543797734652 > libm gives -0x1.8p-55 > mpfr gives -0x1.af74bfa0f1304p-56 If I understand correctly, the *intent* is to give an error bounded by 3 ulp, i.e. an error up to 3 ulp is not something that the user should expect to be "fixed". Perhaps the glibc manual should provide a way to find known bugs more easily. That said, typing "y0" in bugzilla immediately gives https://sourceware.org/bugzilla/show_bug.cgi?id=16492 (for some other functions, which are also common words, this is not that obvious). -- Vincent Lefèvre - Web: 100% accessible validated (X)HTML - Blog: Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)