[PATCH] Fix cos computation for multiple precision fallback (bz #20357)

[Siddhesh Poyarekar]

On Mon, Jul 18, 2016 at 09:47:43AM -0500, Paul E. Murphy wrote:
> > diff --git a/sysdeps/ieee754/dbl-64/s_sin.c b/sysdeps/ieee754/dbl-64/s_sin.c
> > index ca2532f..7c9a079 100644
> > --- a/sysdeps/ieee754/dbl-64/s_sin.c
> > +++ b/sysdeps/ieee754/dbl-64/s_sin.c
> > @@ -803,7 +803,7 @@ sloww (double x, double dx, double orig, int k)
> >    a = t - y;
> >    da = ((t - a) - y) + da;
> > 
> > -  if (n == 2 || n == 1)
> > +  if (n & 2)
> 
> That looks ok.  I had to do double check the unification.  It wasn't
> immediately obvious this was correct.

Yeah, the n == 1 check in csloww had thrown me off the last time - it
is because the input to csloww was always in quadrant 0 or 1 (0.855469
<|x| <2.426265) and hence the check for n == 2 is unnecessary in that
context.  Rotating that by pi/2 for sin is consistent with the n & 2
check.

> > @@ -817,7 +817,7 @@ sloww (double x, double dx, double orig, int k)
> >    if (w[0] == w[0] + cor)
> >      return (a > 0) ? w[0] : -w[0];
> > 
> > -  return (n & 1) ? __mpcos (orig, 0, true) : __mpsin (orig, 0, true);
> > +  return k ? __mpcos (orig, 0, true) : __mpsin (orig, 0, true);
> 
> OK, that fix looks fairly obvious after reviewing commit
> b300455644e2945da05eb49d12d3a037f1408be1.

Thanks.  Adhemerval, do you want to take another look at this or is it
OK if I commit it?

Siddhesh