From: Akila Welihinda <akilawelihinda@g.ucla.edu>
To: Paul Zimmermann <paul.zimmermann@inria.fr>
Cc: libc-alpha@sourceware.org
Subject: Re: [PATCH] sysdeps: Update Taylor Series formula in comment
Date: Sun, 12 Dec 2021 08:50:04 -0800 [thread overview]
Message-ID: <CAHmzmeziNvMOEPd99kCnXmCzcbswaFQRfGO01+VYDe+6QHpOFw@mail.gmail.com> (raw)
In-Reply-To: <mwsfuynxf2.fsf@tomate.loria.fr>
Thanks for taking a look! I think changing a -> x and da -> dx is a good
idea since it looks like we always center the Taylor Series around 0. So I
think the TAYLOR_SIN macro only needs x, dx, and xx as its input. I'll make
this change soon.
On Sat, Dec 11, 2021 at 10:35 PM Paul Zimmermann <Paul.Zimmermann@inria.fr>
wrote:
> Dear Akila,
>
> this change looks good to me.
>
> To make the code clearer, what do you think of changing 'a' into 'x' in
> the macro TAYLOR_SIN (and 'da' to 'dx')?
>
> Paul Zimmermann
>
> > From: Akila Welihinda <akilawelihinda@ucla.edu>
> > Date: Sat, 11 Dec 2021 10:02:14 -0800
> > Cc: Akila Welihinda <akilawelihinda@ucla.edu>
> >
> > The macro TAYLOR_SIN adds the term `-0.5*da*a^2 + da` in hopes
> > of regaining some precision as a function of da. However the
> > comment says we add the term `-0.5*da*a^2 + 0.5*da` which is
> > different. This fix just updates the comment to reflect the
> > code.
> >
> > Signed-off-by: Akila Welihinda <akilawelihinda@ucla.edu>
> > ---
> > sysdeps/ieee754/dbl-64/s_sin.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/sysdeps/ieee754/dbl-64/s_sin.c
> b/sysdeps/ieee754/dbl-64/s_sin.c
> > index 7d89e3dfc2..31e08e3a70 100644
> > --- a/sysdeps/ieee754/dbl-64/s_sin.c
> > +++ b/sysdeps/ieee754/dbl-64/s_sin.c
> > @@ -53,7 +53,7 @@
> > /* The computed polynomial is a variation of the Taylor series
> expansion for
> > sin(a):
> >
> > - a - a^3/3! + a^5/5! - a^7/7! + a^9/9! + (1 - a^2) * da / 2
> > + a - a^3/3! + a^5/5! - a^7/7! + a^9/9! - da*a^2/2 + da
> >
> > The constants s1, s2, s3, etc. are pre-computed values of 1/3!, 1/5!
> and so
> > on. The result is returned to LHS. */
> > --
> > 2.30.1 (Apple Git-130)
>
next prev parent reply other threads:[~2021-12-12 16:50 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-11 18:02 Akila Welihinda
2021-12-12 6:34 ` Paul Zimmermann
2021-12-12 16:50 ` Akila Welihinda [this message]
2021-12-12 18:35 ` [PATCH] sysdeps: Simplify sin Taylor Series calculation Akila Welihinda
2021-12-13 9:53 ` Paul Zimmermann
2021-12-13 14:08 ` Siddhesh Poyarekar
2021-12-13 14:31 ` Paul Zimmermann
2021-12-13 16:58 ` Akila Welihinda
2021-12-11 22:50 [PATCH] sysdeps: Update Taylor Series formula in comment Akila Welihinda
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