Re: why not consfold sin(const)

[kaih@khms.westfalen.de (Kai Henningsen)]

zack@codesourcery.com (Zack Weinberg)  wrote on 19.09.04 in <87oek257mp.fsf@codesourcery.com>:

> Luchezar Belev <l_belev@yahoo.com> writes:
>
> >> Yes, but it does not stretch as far as giving complete junk results,
> >> which is what would happen in some cases if you used host functions.
> >
> > I see. I'm surprised that in the compiler there is no sin/cos/log/etc.
> > funcs already implemented for other reasons.
>
> I'm not sure about exp/log, but trigonometric functions are
> substantially harder to implement with accuracy over their entire
> domain (i.e. the range of the floating-point type) - to do argument
> reduction, glibc has a table giving 2/pi to 5628 hexadecimal digits!
>
> This is the sort of thing where we'd probably take a patch if someone
> wrote one, but we don't consider it very important, certainly not
> compared to how hard it would be to code.  And I think you are
> seriously underestimating the difficulty.

I'd expect that looking into stuff like that would get much more  
interesting if gcc had gmp+mpfr regularly available (as opposed to only  
gfortran using it as an external library).

MfG Kai