From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/3305 Path: news.gmane.org!not-for-mail From: Szabolcs Nagy Newsgroups: gmane.linux.lib.musl.general Subject: Re: Using float_t and double_t in math functions Date: Thu, 9 May 2013 15:21:57 +0200 Message-ID: <20130509132157.GF12689@port70.net> References: <20130509014327.GA6338@brightrain.aerifal.cx> Reply-To: musl@lists.openwall.com NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: ger.gmane.org 1368105730 3277 80.91.229.3 (9 May 2013 13:22:10 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 9 May 2013 13:22:10 +0000 (UTC) To: musl@lists.openwall.com Original-X-From: musl-return-3309-gllmg-musl=m.gmane.org@lists.openwall.com Thu May 09 15:22:10 2013 Return-path: Envelope-to: gllmg-musl@plane.gmane.org Original-Received: from mother.openwall.net ([195.42.179.200]) by plane.gmane.org with smtp (Exim 4.69) (envelope-from ) id 1UaQnR-00052Y-L9 for gllmg-musl@plane.gmane.org; Thu, 09 May 2013 15:22:09 +0200 Original-Received: (qmail 21962 invoked by uid 550); 9 May 2013 13:22:09 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: Original-Received: (qmail 21954 invoked from network); 9 May 2013 13:22:09 -0000 Content-Disposition: inline In-Reply-To: <20130509014327.GA6338@brightrain.aerifal.cx> User-Agent: Mutt/1.5.21 (2010-09-15) Xref: news.gmane.org gmane.linux.lib.musl.general:3305 Archived-At: * Rich Felker [2013-05-08 21:43:27 -0400]: > As far as I can tell, in most of the affected code, keeping excess > precision does not hurt the accuracy of the result, and it might even > improve the results. Thus, nsz and I discussed (on IRC) the > possibility of changing intermediate variables in functions that can > accept excess precision from float and double to float_t and double_t. > This would not affect the generated code at all on machines without > excess precision, but on x86 (without SSE) it eliminates all the > costly store/load pairs. As an example (on my test machine), it ie. it is only for i386 (without sse) (which is not a trendy platform nowadays) but there it improves performance and code size a bit so it is worth doing at the same time all the STRICT_ASSIGN macros can be removed (already a noop) which were there to enforce store with the right precision on i386 when musl is compiled without -ffloat-store, but i dont think that should be supported btw the other ugly macro that remains is FORCE_EVAL to force evaluation of floating-point expressions for their side-effect, which should be eventually #define FORCE_EVAL(expr) do{ \ _Pragma("STDC FENV_ACCESS ON") \ expr; \ } while(0) but no compiler supports this that i know of so now we have volatile hacks with unnecessary stores there are a few more 'volatile' in the code but all should be possible to clean up (fma and fmaf are probably exceptions similar to FORCE_EVAL)