Dmitry Karasik wrote:
> #include <math.h>
> #include <stdio.h>
> int main( int argc, char ** argv)
> {
> double g = (double) 3.1415926535897900074;
> printf("sin(%.10g)=%.10g\n", g, sin(g));
> }
>
> output is :
>
> sin(3.141592654)=3.231089149e-15
>
> whereas all other sin() implementation I could find ( freebsd, linux, msvc)
> report this:
>
> sin(3.141592654)=3.231085104e-015
>
> the difference is in 7th digit, and is significant for double precision.
This appears to be due to an approximation in __kernel_sin in which if
|x| < 2**-27 the approximation sin(x) ~ x is used.
<http://sourceware.org/cgi-bin/cvsweb.cgi/~checkout~/src/newlib/libm/math/k_sin.c?content-type=text/plain&cvsroot=src>.
This code seems to be completely untouched since the original import
into CVS in 2000, so I'm guessing it's a very old implementation. I'm
not sure how we'd go about fixing this other than to look for a more
sophisticated implementation and contribute it to newlib.
In any case this is more of a newlib issue than a Cygwin issue as we are
just a consumer of this code, so followups should go to the newlib list.
Brian
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