X-Git-Url: http://erislabs.net/gitweb/?a=blobdiff_plain;f=lib%2Fsignbitf.c;h=8b0f93c9e9c6ce70004ee0ba447b516b3b59d7dd;hb=4565266f776db0d78b2c207a5fe79f929f9806ca;hp=c172b5fbefbc6f323fac60a0caa0066aee1242e4;hpb=f8cce822d6a82cadf0ea2907eb94a1017910322f;p=gnulib.git

diff --git a/lib/signbitf.c b/lib/signbitf.c
index c172b5fbe..8b0f93c9e 100644
--- a/lib/signbitf.c
+++ b/lib/signbitf.c
@@ -1,19 +1,18 @@
 /* signbit() macro: Determine the sign bit of a floating-point number.
    Copyright (C) 2007 Free Software Foundation, Inc.
 
-   This program is free software; you can redistribute it and/or modify
+   This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
-   the Free Software Foundation; either version 2, or (at your option)
-   any later version.
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
 
    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.
 
-   You should have received a copy of the GNU General Public License along
-   with this program; if not, write to the Free Software Foundation,
-   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
 
 #include <config.h>
 
@@ -30,11 +29,19 @@ int
 gl_signbitf (float arg)
 {
 #if defined FLT_SIGNBIT_WORD && defined FLT_SIGNBIT_BIT
+  /* The use of a union to extract the bits of the representation of a
+     'long double' is safe in practice, despite of the "aliasing rules" of
+     C99, because the GCC docs say
+       "Even with '-fstrict-aliasing', type-punning is allowed, provided the
+        memory is accessed through the union type."
+     and similarly for other compilers.  */
 # define NWORDS \
     ((sizeof (float) + sizeof (unsigned int) - 1) / sizeof (unsigned int))
   union { float value; unsigned int word[NWORDS]; } m;
   m.value = arg;
   return (m.word[FLT_SIGNBIT_WORD] >> FLT_SIGNBIT_BIT) & 1;
+#elif HAVE_COPYSIGNF_IN_LIBC
+  return copysignf (1.0f, arg) < 0;
 #else
   /* This does not do the right thing for NaN, but this is irrelevant for
      most use cases.  */