[newlib-cygwin] sqrt: Fix NaN propagation for IEEE Std 754-2008
Corinna Vinschen
corinna@sourceware.org
Mon Aug 22 12:21:00 GMT 2016
https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=96fc528397f02a8ac36cfd66179fed815d3ab527
commit 96fc528397f02a8ac36cfd66179fed815d3ab527
Author: Ray Donnelly <mingw.android@gmail.com>
Date: Wed Apr 6 02:59:53 2016 +0100
sqrt: Fix NaN propagation for IEEE Std 754-2008
The R language has some hacks specifically for mingw-w64 that
were caused by our handling of NaNs in sqrt(x). R uses a
special valued NaN to mean 'Not Available' and expects it to
be retained through various calculations. Our sqrt(x) doesn't
do this, instead it normalises such a NaN (retaining sign).
From:
http://wwwf.imperial.ac.uk/~drmii/M3SC_2016/IEEE_2008_4610935.pdf
"6.2.3 NaN propagation
An operation that propagates a NaN operand to its result and
has a single NaN as an input should produce a NaN with the
payload of the input NaN if representable in the destination
format."
There might even be a slight speed-up from this too.
Thanks to Duncan Murdoch for finding the reference.
Diff:
---
winsup/cygwin/math/sqrt.def.h | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/winsup/cygwin/math/sqrt.def.h b/winsup/cygwin/math/sqrt.def.h
index 1048130..2690d1d 100644
--- a/winsup/cygwin/math/sqrt.def.h
+++ b/winsup/cygwin/math/sqrt.def.h
@@ -73,9 +73,8 @@ __FLT_ABI (sqrt) (__FLT_TYPE x)
if (x_class == FP_ZERO)
return __FLT_CST (-0.0);
- res = (signbit (x) ? -__FLT_NAN : __FLT_NAN);
- __FLT_RPT_DOMAIN ("sqrt", x, 0.0, res);
- return res;
+ __FLT_RPT_DOMAIN ("sqrt", x, 0.0, x);
+ return x;
}
else if (x_class == FP_ZERO)
return __FLT_CST (0.0);
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