From nobody Mon Sep 06 18:04:59 2021 X-Original-To: freebsd-current@mlmmj.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mlmmj.nyi.freebsd.org (Postfix) with ESMTP id 297EB17A4D2C for ; Mon, 6 Sep 2021 18:05:02 +0000 (UTC) (envelope-from sgk@troutmask.apl.washington.edu) Received: from troutmask.apl.washington.edu (troutmask.apl.washington.edu [128.95.76.21]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256 client-signature RSA-PSS (2048 bits) client-digest SHA256) (Client CN "troutmask", Issuer "troutmask" (not verified)) by mx1.freebsd.org (Postfix) with ESMTPS id 4H3GWx5x2xz4gDn; Mon, 6 Sep 2021 18:05:01 +0000 (UTC) (envelope-from sgk@troutmask.apl.washington.edu) Received: from troutmask.apl.washington.edu (localhost [127.0.0.1]) by troutmask.apl.washington.edu (8.16.1/8.16.1) with ESMTPS id 186I4xk1087714 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NO); Mon, 6 Sep 2021 11:05:00 -0700 (PDT) (envelope-from sgk@troutmask.apl.washington.edu) Received: (from sgk@localhost) by troutmask.apl.washington.edu (8.16.1/8.16.1/Submit) id 186I4x57087713; Mon, 6 Sep 2021 11:04:59 -0700 (PDT) (envelope-from sgk) Date: Mon, 6 Sep 2021 11:04:59 -0700 From: Steve Kargl To: Mark Murray Cc: freebsd-current@freebsd.org Subject: Re: BUG in libm's powf Message-ID: <20210906180459.GA87487@troutmask.apl.washington.edu> References: <20210906152836.GA86615@troutmask.apl.washington.edu> <01D81389-45D1-4278-8DC1-7995D34D0276@FreeBSD.org> <20210906175318.GA87474@troutmask.apl.washington.edu> List-Id: Discussions about the use of FreeBSD-current List-Archive: https://lists.freebsd.org/archives/freebsd-current List-Help: List-Post: List-Subscribe: List-Unsubscribe: Sender: owner-freebsd-current@freebsd.org MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 4H3GWx5x2xz4gDn X-Spamd-Bar: ---- Authentication-Results: mx1.freebsd.org; none X-Spamd-Result: default: False [-4.00 / 15.00]; REPLY(-4.00)[] X-ThisMailContainsUnwantedMimeParts: N No, thank you for the quick response. Of course, a one character diff might be easier to review. :-) -- steve On Mon, Sep 06, 2021 at 06:55:07PM +0100, Mark Murray wrote: > Thanks! > > And it's committed! > > M > > > On 6 Sep 2021, at 18:53, Steve Kargl wrote: > > > > Fine with me. I don't have a phabricator account and > > bugzilla reports seems to get lost in the ether. > > > > -- > > steve > > > > On Mon, Sep 06, 2021 at 06:45:11PM +0100, Mark Murray wrote: > >> Hi > >> > >> I've opened a Phab ticket for this. I hope that's OK? > >> > >> https://reviews.freebsd.org/D31865 > >> > >> M > >> > >>> On 6 Sep 2021, at 16:28, Steve Kargl wrote: > >>> > >>> Paul Zimmermann has identified a bug in Openlibm's powf(), > >>> which is identical to FreeBSD's libm. Both derived from > >>> fdlibm. https://github.com/JuliaMath/openlibm/issues/212. > >>> > >>> Consider > >>> > >>> % cat h.c > >>> #include > >>> #include > >>> int > >>> main(void) > >>> { > >>> float x, y, z; > >>> x = 0x1.ffffecp-1F; > >>> y = -0x1.000002p+27F; > >>> z = 0x1.557a86p115F; > >>> printf("%e %e %e <-- should be %e\n", x, y, powf(x,y), z); > >>> return 0; > >>> } > >>> > >>> % cc -o h -fno-builtin h.c -lm && ./h > >>> 9.999994e-01 -1.342177e+08 inf <-- should be 5.540807e+34 > >>> > >>> Note, clang seems to have a builtin for powf(), but one cannot > >>> count of clang being the only consumer of libm. With the patch > >>> at the end of this email, I get > >>> > >>> % cc -o h -fno-builtin h.c -L/home/kargl/trunk/math/libm/msun -lmath && ./h > >>> 9.999994e-01 -1.342177e+08 5.540807e+34 <-- should be 5.540807e+34 > >>> > >>> Watch for copy and paste whitespace corruption. > >>> > >>> --- /usr/src/lib/msun/src/e_powf.c 2021-02-21 03:29:00.956878000 -0800 > >>> +++ src/e_powf.c 2021-09-06 08:17:09.800008000 -0700 > >>> @@ -136,7 +136,7 @@ > >>> /* |y| is huge */ > >>> if(iy>0x4d000000) { /* if |y| > 2**27 */ > >>> /* over/underflow if x is not close to one */ > >>> - if(ix<0x3f7ffff7) return (hy<0)? sn*huge*huge:sn*tiny*tiny; > >>> + if(ix<0x3f7ffff6) return (hy<0)? sn*huge*huge:sn*tiny*tiny; > >>> if(ix>0x3f800007) return (hy>0)? sn*huge*huge:sn*tiny*tiny; > >>> /* now |1-x| is tiny <= 2**-20, suffice to compute > >>> log(x) by x-x^2/2+x^3/3-x^4/4 */ > >>> > >>> > >>> -- > >>> Steve > >>> > >> > >> -- > >> Mark R V Murray > >> > > > > > > > > -- > > Steve > > > > -- > Mark R V Murray > -- Steve