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Re: 1.5.24: sin() bug
- From: Brian Dessent <brian at dessent dot net>
- To: newlib at sourceware dot org
- Cc: cygwin at cygwin dot com
- Date: Wed, 29 Aug 2007 10:06:38 -0700
- Subject: Re: 1.5.24: sin() bug
- References: <20070829153331.GA95558@tetsuo.karasik.eu.org>
- Reply-to: cygwin at cygwin dot com
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 :
> whereas all other sin() implementation I could find ( freebsd, linux, msvc)
> report this:
> 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.
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.
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