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[Bug math/14412] Removal of sysdeps/x86_64/fpu/s_sincos.S causes regressions
- From: "wbrana at gmail dot com" <sourceware-bugzilla at sourceware dot org>
- To: glibc-bugs at sourceware dot org
- Date: Mon, 29 Apr 2013 12:32:34 +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 #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 Â2^63 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.
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