From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/13484 Path: news.gmane.org!.POSTED!not-for-mail From: Rich Felker Newsgroups: gmane.linux.lib.musl.general Subject: Re: 32-bit double and long double Date: Mon, 26 Nov 2018 21:32:11 -0500 Message-ID: <20181127023211.GR23599@brightrain.aerifal.cx> References: <87va4j3lpr.fsf@southeast> <20181126170339.GO23599@brightrain.aerifal.cx> Reply-To: musl@lists.openwall.com NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: blaine.gmane.org 1543285819 31274 195.159.176.226 (27 Nov 2018 02:30:19 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Tue, 27 Nov 2018 02:30:19 +0000 (UTC) User-Agent: Mutt/1.5.21 (2010-09-15) To: musl@lists.openwall.com Original-X-From: musl-return-13500-gllmg-musl=m.gmane.org@lists.openwall.com Tue Nov 27 03:30:15 2018 Return-path: Envelope-to: gllmg-musl@m.gmane.org Original-Received: from mother.openwall.net ([195.42.179.200]) by blaine.gmane.org with smtp (Exim 4.84_2) (envelope-from ) id 1gRT8h-00081U-8K for gllmg-musl@m.gmane.org; Tue, 27 Nov 2018 03:30:15 +0100 Original-Received: (qmail 1212 invoked by uid 550); 27 Nov 2018 02:32:24 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Original-Received: (qmail 1193 invoked from network); 27 Nov 2018 02:32:23 -0000 Content-Disposition: inline In-Reply-To: Original-Sender: Rich Felker Xref: news.gmane.org gmane.linux.lib.musl.general:13484 Archived-At: On Mon, Nov 26, 2018 at 05:36:58PM +0000, Jon Chesterfield wrote: > > > > Is there a reason your target is defining double in an unuseful and > > incompatible way rather than doing hard-single and soft-double? If you > > have any control over the choice of ABI, I think the latter makes a > > lot more sense. > > > > I can see a few arguments for float==double, but haven't actually done that > for our target yet. > > A common error is to write 1.0 instead of 1.0f, where the former sometimes > pulls in the soft double support. I think gcc has a language-variant option to make floating point constants float by default rather than double, but this is probably a bad idea. Better would be just setting up your tooling to catch inadvertent use of double where it's not wanted/needed. > Integer arguments to libm functions promote to double but I would prefer > promote to 32 bit float. This is only the case if you're calling the functions that take double arguments. If you call the float ones, promotion is just to float. It's your choice which you use. > Arguments to variadic functions promote to double. Again I would prefer 32 > bit float. Indeed this is a hard limitation of the language. I suppose it comes in mostly/only for passing floating point values to printf. The promotion should at least be nothing more than a few 64-bit shift/or ops. Rich