From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-3.0 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED,RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL autolearn=ham autolearn_force=no version=3.4.2 Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by inbox.vuxu.org (OpenSMTPD) with SMTP id f91bc5a1 for ; Tue, 14 Jan 2020 19:53:54 +0000 (UTC) Received: (qmail 8191 invoked by uid 550); 14 Jan 2020 19:53:53 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Reply-To: musl@lists.openwall.com Received: (qmail 8173 invoked from network); 14 Jan 2020 19:53:52 -0000 Date: Tue, 14 Jan 2020 22:53:41 +0300 (MSK) From: Alexander Monakov To: musl@lists.openwall.com In-Reply-To: <20200114185835.GG30412@brightrain.aerifal.cx> Message-ID: References: <20200114185058.GV23985@port70.net> <20200114185835.GG30412@brightrain.aerifal.cx> User-Agent: Alpine 2.20.13 (LNX 116 2015-12-14) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Subject: Re: [musl] Q: dealing with missing removal of excess precision On Tue, 14 Jan 2020, Rich Felker wrote: > > otoh it would be nice if there was a way to tell the compiler not to > > remove it (e.g. in case the asm already took care of it) even in c99 > > standard mode. > > Perhaps this happens if the output constraint is tied to a float > rather than a long double? Precisely. That's what previously posted patches do, and they match existing hand-tuned assembly. I misspoke when saying that Glibc might return a value with excess precision. I was looking at fmod-like functions and missed a slightly subtle point that fprem does not introduce excess precision. So I don't actually have any example where Glibc might misbehave in that regard. Alexander