Fix ldbl-128ibm nearbyintl use of signaling comparisons on NaNs (bug 18857).

The ldbl-128ibm implementation of nearbyintl wrongly uses signaling
comparisons such as "if (fabs (u.d[0].d) < TWO52)" on arguments that
might be NaNs, when "invalid" exceptions should not be raised.  (For
hard float, this issue may be hidden by
<https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58684>, powerpc GCC
wrongly only using unordered comparison instructions.)  This patch
fixes this by just returning the argument if it is not finite (because
of the arbitrary value of the low part of a NaN in IBM long double,
there are quite a lot of comparisons that could end up involving a NaN
when the argument to nearbyintl is a NaN, so excluding NaN arguments
at the start is the simplest and safest fix).

Tested for powerpc-nofpu, where it removes failures for spurious
"invalid" exceptions from nearbyintl.

	[BZ #18857]
	* sysdeps/ieee754/ldbl-128ibm/s_nearbyintl.c (__nearbyintl): Just
	return non-finite argument without doing ordered comparisons on
	it.

diff --git a/ChangeLog b/ChangeLog
index fd281993c84fd0d72c5a88c6fe0859fc3118ab01..5053bf31d5e9d60e372302acc9141f4bc61e01c8 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,10 @@
 2015-09-15  Joseph Myers  <joseph@codesourcery.com>
 
+       [BZ #18857]
+       * sysdeps/ieee754/ldbl-128ibm/s_nearbyintl.c (__nearbyintl): Just
+       return non-finite argument without doing ordered comparisons on
+       it.
+
        [BZ #16296]
        * math/fenv.h (fegetround): Use __attribute_pure__.
        * include/fenv.h (__fegetround): Likewise.

diff --git a/NEWS b/NEWS
index b35d5424d38dec55c6c2552d710ccb4acc59472d..5db57a2e9a5d40978f1b36b783ad34a3ff8f43f7 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -13,8 +13,8 @@ Version 2.23
   16519, 16520, 16521, 16734, 16973, 16985, 17787, 17905, 18084, 18086,
   18240, 18265, 18370, 18421, 18480, 18525, 18595, 18610, 18618, 18647,
   18661, 18674, 18675, 18681, 18757, 18778, 18781, 18787, 18789, 18790,
-  18795, 18796, 18820, 18823, 18824, 18863, 18870, 18873, 18875, 18887,
-  18921, 18952, 18961, 18966.
+  18795, 18796, 18820, 18823, 18824, 18857, 18863, 18870, 18873, 18875,
+  18887, 18921, 18952, 18961, 18966.
 
 * The obsolete header <regexp.h> has been removed.  Programs that require
   this header must be updated to use <regex.h> instead.

diff --git a/sysdeps/ieee754/ldbl-128ibm/s_nearbyintl.c b/sysdeps/ieee754/ldbl-128ibm/s_nearbyintl.c
index 5f92a5fee845dec0f94c9d332b78e0f1d163c503..99f47473b9c61e78efea2f12dab0bf7c3c804b37 100644 (file)
--- a/sysdeps/ieee754/ldbl-128ibm/s_nearbyintl.c
+++ b/sysdeps/ieee754/ldbl-128ibm/s_nearbyintl.c
@@ -36,7 +36,9 @@ __nearbyintl (long double x)
   union ibm_extended_long_double u;
   u.ld = x;
 
-  if (fabs (u.d[0].d) < TWO52)
+  if (!isfinite (u.d[0].d))
+    return x;
+  else if (fabs (u.d[0].d) < TWO52)
     {
       double xh = u.d[0].d;
       double high = u.d[0].d;