From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/14708 Path: news.gmane.org!.POSTED.blaine.gmane.org!not-for-mail From: Szabolcs Nagy Newsgroups: gmane.linux.lib.musl.general Subject: Re: [PATCH] math: optimize lrint on 32bit targets Date: Mon, 23 Sep 2019 16:54:23 +0200 Message-ID: <20190923145423.GD22009@port70.net> References: <20190921155234.GA22009@port70.net> <20190922204335.GC22009@port70.net> <20190923142436.GL9017@brightrain.aerifal.cx> Reply-To: musl@lists.openwall.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Injection-Info: blaine.gmane.org; posting-host="blaine.gmane.org:195.159.176.226"; logging-data="68329"; mail-complaints-to="usenet@blaine.gmane.org" User-Agent: Mutt/1.10.1 (2018-07-13) To: musl@lists.openwall.com Original-X-From: musl-return-14724-gllmg-musl=m.gmane.org@lists.openwall.com Mon Sep 23 16:54:39 2019 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 4.89) (envelope-from ) id 1iCPja-000Hg6-Da for gllmg-musl@m.gmane.org; Mon, 23 Sep 2019 16:54:38 +0200 Original-Received: (qmail 32713 invoked by uid 550); 23 Sep 2019 14:54:36 -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 32695 invoked from network); 23 Sep 2019 14:54:35 -0000 Mail-Followup-To: musl@lists.openwall.com Content-Disposition: inline In-Reply-To: <20190923142436.GL9017@brightrain.aerifal.cx> Xref: news.gmane.org gmane.linux.lib.musl.general:14708 Archived-At: * Rich Felker [2019-09-23 10:24:36 -0400]: > On Sun, Sep 22, 2019 at 10:43:35PM +0200, Szabolcs Nagy wrote: > > +long lrint(double x) > > +{ > > + uint32_t abstop = asuint64(x)>>32 & 0x7fffffff; > > + uint64_t sign = asuint64(x) & (1ULL << 63); > > + > > + if (abstop < 0x41dfffff) { > > + /* |x| < 0x7ffffc00, no overflow */ > > + double_t toint = asdouble(asuint64(1/EPS) | sign); > > + double_t y = x + toint - toint; > > + return (long)y; > > + } > > + return lrint_slow(x); > > +} > > #else > > long lrint(double x) > > { > > -- > > Looks good! Thanks for working on this. > > Does asuint64(1/EPS) compile to an integer constant rather than > needing to load a floating point operand? I would assume so but just > want to check, since otherwise it might make more sense to write this > as an expression involving [L]DBL_MANT_DIG and integer bitshifts. i think if 1/EPS was rounding mode dependent then it would be computed at runtime, but since it's an exact power-of-two gcc const folds it (on arm there is no load, the value is put together by bitops with immediates)