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Date:      Thu, 27 Jun 2013 09:12:04 -0700
From:      enh <enh@google.com>
To:        Steve Kargl <sgk@troutmask.apl.washington.edu>
Cc:        freebsd-numerics@freebsd.org
Subject:   Re: sincos?
Message-ID:  <CAJgzZoqbF-bS6M8OYmVx7=eKfpNmavXXZXX0Zgvsxr07CUfC0w@mail.gmail.com>
In-Reply-To: <20130627013502.GA37295@troutmask.apl.washington.edu>
References:  <CAJgzZopTzfYXecu7zRKhVNEEBOCtz8Z2qK8ka74c5LKZxC8mEw@mail.gmail.com> <20130627013502.GA37295@troutmask.apl.washington.edu>

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well, that was Intel and the code's not been accepted, but yes --- that's
another reason for me not to accept their patch!

Intel claimed "The reason for this fix [beside workaround for O0 switch] -
it helps to remove some sin[f]+cos[f] code duplication (which is the whole
reason for introduction of such function at all), which results in
1.58-1.81x performance gain on intervals |x|<100." i've not seen their
benchmark code, so i don't know what their distribution of values was, and
i don't understand why they covered a range as large as +/- 100.

when looking at i7 performance though, remember that x86 Android will
usually be running on Atom (and most Android devices are actually ARM, not
x86).

On Wed, Jun 26, 2013 at 6:35 PM, Steve Kargl <
sgk@troutmask.apl.washington.edu> wrote:

> On Wed, Jun 26, 2013 at 04:45:34PM -0700, enh wrote:
> > i'm a recent lurker on this list; i've inherited Android's C library, and
> > among other things i'm trying to track FreeBSD's lib/msun much more
> closely
> > than we have traditionally.
> >
> > i was just reminded of the existence of a change submitted to us
> (Android)
> > a while back that adds a sincos/sincosf implementation cobbled together
> > from your s_sin.c/s_sinf.c and s_cos.c/s_cosf.c implementations:
> > https://android-review.googlesource.com/#/c/47585/<;
> https://android-review.googlesource.com/#/c/47585/1>;
> >
>
> A quick glance at the code shows that the android project has
> slapped its Copyright on fdlibm code.  I suspect that you'll
> want to restore proper attribution to Sun Microsystems.
>
> > the submitter (Intel) rightly points out that at the moment GCC carefully
> > optimizes paired sin/cos calls into a sincos call which we deoptimize
> back
> > into separate sin/cos calls. i personally don't want to take on
> maintenance
> > of this, but i would be happy to include you guys' sincos implementation
> if
> > you had one. is there a reason you don't have one?
>
> I haven't submitted the versions of sincos[fl], which I've
> developed over the last year or so, yet.  First, I need to
> redo some testing.  Second, I need to convince Bruce that
> the implementation would be a nice addition to libm.
>
> --
> Steve
>



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