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 c72728cb for ; Sun, 19 Jan 2020 09:08:11 +0000 (UTC) Received: (qmail 1878 invoked by uid 550); 19 Jan 2020 09:08:10 -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 1860 invoked from network); 19 Jan 2020 09:08:09 -0000 X-Authentication-Warning: key0.esi.com.au: damianm owned process doing -bs Date: Sun, 19 Jan 2020 20:07:56 +1100 (AEDT) From: Damian McGuckin To: musl@lists.openwall.com In-Reply-To: <20200117145350.GR30412@brightrain.aerifal.cx> Message-ID: References: <20200116161427.GO30412@brightrain.aerifal.cx> <20200116193343.GP30412@brightrain.aerifal.cx> <20200117145350.GR30412@brightrain.aerifal.cx> User-Agent: Alpine 2.02 (LRH 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Subject: Re: [musl] Considering x86-64 fenv.s to C On Fri, 17 Jan 2020, Rich Felker wrote: >> x86_64 >> >> * In assembler >> >> * Why does 'feclearexcept' disrespect the flags by clearing ALL x86 bits? > > As you said above, updating x87 status register is expensive because > the only way to write it is to read-modify-write the whole fenv. But > since we know on x86_64 we have sse registers, we can just move all > the flags to the sse register, then use fnclex to clear the x87 one > inexpensively, and the effective set of raised flags remains the same. I am worried about the lack of consistency. What if something that is only using (say) 80-bit floating arithmetic comes back looking for a raised exception in the x87 status register & MUSL has moved effectively moved it to the mxcsr. Mind you, I think that BSD is guilty of almost the same error in rounding modes. Regards - Damian Pacific Engineering Systems International, 277-279 Broadway, Glebe NSW 2037 Ph:+61-2-8571-0847 .. Fx:+61-2-9692-9623 | unsolicited email not wanted here Views & opinions here are mine and not those of any past or present employer