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[Bug math/14412] Removal of sysdeps/x86_64/fpu/s_sincos.S causes regressions
- From: "bugdal at aerifal dot cx" <sourceware-bugzilla at sourceware dot org>
- To: glibc-bugs at sourceware dot org
- Date: Mon, 29 Apr 2013 13:51:50 +0000
- Subject: [Bug math/14412] Removal of sysdeps/x86_64/fpu/s_sincos.S causes regressions
- Auto-submitted: auto-generated
- References: <bug-14412-131 at http dot sourceware dot org/bugzilla/>
http://sourceware.org/bugzilla/show_bug.cgi?id=14412
--- Comment #37 from Rich Felker <bugdal at aerifal dot cx> 2013-04-29 13:51:50 UTC ---
At the outer edges of that range, the error is "only" around 1000 ulps. This
isn't correct, but at least it's better than just having 4 or 5 bits of
precision (or none at all). Since the x87 internally uses a 66-bit
representation of pi, and doubles are 52-bit, I suspect precision starts to
trail off around 16384*pi, but it will be bad even for much smaller values when
the result is close to zero.
Experimentally, 0x1p18 seems to be the first power of two for which the result
is wrong within 15 decimal places, but 0x1p14*M_PI is already badly wrong (only
the first 4 decimal places are correct).
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