Use of C99 extra long double math functions after r236148
sgk at troutmask.apl.washington.edu
Tue May 29 00:07:56 UTC 2012
On Mon, May 28, 2012 at 06:44:42PM -0500, Stephen Montgomery-Smith wrote:
> On 05/28/2012 06:30 PM, Steve Kargl wrote:
> >>From clog.c in http://www.netlib.org/cephes/c9x-complex
> >double complex
> >ccosh (z)
> > double complex z;
> > double complex w;
> > double x, y;
> > x = creal(z);
> > y = cimag(z);
> > w = cosh (x) * cos (y) + (sinh (x) * sin (y)) * I;
> > return (w);
> >See math_private.h about the above.
> I looked in math_private.h - I presume you meant
> lib/msun/src/math_private.h. I wasn't able to find anything about ccosh
> I think that for a rough and ready ccosh, this is high enough quality
> for a math/cephes port.
That's the problem. It is not acceptable (imo). The comment in
math_private.h that is relevant is
* Inline functions that can be used to construct complex values.
* The C99 standard intends x+I*y to be used for this, but x+I*y is
* currently unusable in general since gcc introduces many overflow,
* underflow, sign and efficiency bugs by rewriting I*y as
* (0.0+I)*(y+0.0*I) and laboriously computing the full complex product.
* In particular, I*Inf is corrupted to NaN+I*Inf, and I*-0 is corrupted
* to -0.0+I*0.0.
Those wrong +-0 mean you may up end up on the worng riemann sheet,
and that NaN propagates.
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