Re: [Bug math/14412] Removal of sysdeps/x86_64/fpu/s_sincos.S causes regressions

["Ondřej Bílka" <neleai@seznam.cz>]

On Mon, Apr 29, 2013 at 12:32:34PM +0000, wbrana at gmail dot com wrote:
> http://sourceware.org/bugzilla/show_bug.cgi?id=14412
> 
> --- Comment #28 from wbrana at gmail dot com 2013-04-29 12:32:34 UTC ---
> according to http://sourceware.org/bugzilla/show_bug.cgi?id=13658#c2
> fast functions can be used when source operand is in certain range.
> Slow functions should be used only outside interval.
> 
> "The FPTAN, FSIN, FCOS, and FSINCOS instructions set the C2 flag to 1 to
> indicate that the source operand is beyond the allowable range of ±2^63 and
> clear the C2 flag if the source operand is within the allowable range."
> 
> So, outside the interval [-2^63,+2^63] ("allowable range"), these instructions
> must not be used (or they can be used, but with a fallback if the C2 flag is
> set to 1). But note that the glibc implementation is more accurate, even with
> (very probably) correct rounding, so that it is better to use it anyway.
>
Well results of sin,cos.. with large numbers are pure garbage no matter
what you try. As cos(1.0e18*PI) = cos(1.0e18*PI + PI) you can basicaly print random
number between -1.0 and 1.0 and be correct.