Re: weird optimization in sin+cos, x86 backend

[Andrew Haley <aph at redhat dot com>]

On 02/10/2012 01:30 PM, James Courtier-Dutton wrote:
> On 10 February 2012 10:42, Andrew Haley <aph@redhat.com> wrote:
> 
> I think a starting point would be at least documenting correctly the
> accuracy of the current libm, because what is currently in the
> documents is obviously wrong.
> It certainly does not document that sin() is currently more accurate
> than sinl() on x86_64 platforms, even with -O0.

It isn't.

  cout << scientific << setprecision(20) << sin(0.5) << "\n";
  cout << scientific << setprecision(20) << sinl(0.5) << "\n";
  cout << Sin(Real("0.5")).toString(20,10) << "\n";

gives:

4.79425538604203005377e-01
4.79425538604203000282e-01
4.79425538604203000273e-01

The last one is from MPFR.

In most cases you'll get more accurate results from sinl().

Andrew.