From: Joseph Myers <joseph@codesourcery.com>
To: Paul Zimmermann <Paul.Zimmermann@inria.fr>
Cc: libc-alpha@sourceware.org
Subject: Re: fix inaccuracy of j0f for x >= 2^127 when sin(x)+cos(x) is tiny
Date: Mon, 27 Jul 2020 21:35:29 +0000 [thread overview]
Message-ID: <alpine.DEB.2.21.2007272133330.13114@digraph.polyomino.org.uk> (raw)
In-Reply-To: <mwmu3knale.fsf@tomate.loria.fr>
On Mon, 27 Jul 2020, Paul Zimmermann wrote:
> + float x0 = 3.153646966e+38f;
> + float y = x - x0; /* exact */
> + /* sin(y) = sin(x)*cos(x0)-cos(x)*sin(x0) */
> + z = __sinf (y);
> + float eps = 8.17583368e-8f;
> + /* cos(x0) ~ -sin(x0) + eps */
> + z += eps * __cosf (x);
> + /* now z ~ (sin(x)-cos(x))*cos(x0) */
> + float cosx0 = -0.707106740f;
In new code we generally prefer to use hex float constants in such cases
where a specific floating-point value is wanted.
--
Joseph S. Myers
joseph@codesourcery.com
next prev parent reply other threads:[~2020-07-27 21:35 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-27 17:15 fix inaccuracy of j0f for x >= 2^127 when sin(x)+cos(x) is tiny Paul Zimmermann
2020-07-27 21:35 ` Joseph Myers [this message]
2020-07-28 8:23 ` Paul Zimmermann
2020-07-28 9:19 ` Andreas Schwab
2020-07-28 10:50 ` Paul Zimmermann
2020-07-28 18:09 ` Adhemerval Zanella via Libc-alpha
2020-07-29 7:03 ` fix inaccuracy of j0f for x >= 2^127 when sin(x)+cos(x) is tiny (v2) Paul Zimmermann
2020-07-29 20:25 ` Adhemerval Zanella via Libc-alpha
2020-07-30 7:20 ` fix inaccuracy of j0f for x >= 2^127 when sin(x)+cos(x) is tiny (v3) Paul Zimmermann
2020-07-30 8:53 ` Florian Weimer via Libc-alpha
2020-08-03 13:19 ` fix inaccuracy of j0f for x >= 2^127 when sin(x)+cos(x) is tiny (v4) Paul Zimmermann
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