From: Paul Eggert <eggert@cs.ucla.edu>
Date: Mon, 9 Feb 2015 07:12:04 +0000 (-0800)
Subject: Use C99's INFINITY and NAN macros
X-Git-Tag: emacs-25.0.90~2008^2~54
X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=2f7008715326a49770fcb82003ed78eab28c0626;p=emacs.git

Use C99's INFINITY and NAN macros

* lread.c: Include <math.h>.
(string_to_number): Use INFINITY and NAN rather than rolling our own.
This avoids some runtime diagnostics when building with
gcc -fsanitize=undefined.
---

diff --git a/src/ChangeLog b/src/ChangeLog
index 3b2c9a6777f..381ae6b0989 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,5 +1,11 @@
 2015-02-09  Paul Eggert  <eggert@cs.ucla.edu>
 
+	Use C99's INFINITY and NAN macros
+	* lread.c: Include <math.h>.
+	(string_to_number): Use INFINITY and NAN rather than rolling our own.
+	This avoids some runtime diagnostics when building with
+	gcc -fsanitize=undefined.
+
 	Fix bidi_explicit_dir_char undefined behavior
 	* bidi.c (bidi_explicit_dir_char): Avoid subscript error when
 	argument is BIDI_EOB.  This can happen in bidi_level_of_next_char.
diff --git a/src/lread.c b/src/lread.c
index 69ec05964be..b42849fc414 100644
--- a/src/lread.c
+++ b/src/lread.c
@@ -28,6 +28,7 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #include <sys/file.h>
 #include <errno.h>
 #include <limits.h>	/* For CHAR_BIT.  */
+#include <math.h>
 #include <stat-time.h>
 #include "lisp.h"
 #include "intervals.h"
@@ -3369,10 +3370,6 @@ string_to_number (char const *string, int base, bool ignore_trailing)
   bool float_syntax = 0;
   double value = 0;
 
-  /* Compute NaN and infinities using a variable, to cope with compilers that
-     think they are smarter than we are.  */
-  double zero = 0;
-
   /* Negate the value ourselves.  This treats 0, NaNs, and infinity properly on
      IEEE floating point hosts, and works around a formerly-common bug where
      atof ("-0.0") drops the sign.  */
@@ -3424,30 +3421,15 @@ string_to_number (char const *string, int base, bool ignore_trailing)
 	    {
 	      state |= E_EXP;
 	      cp += 3;
-	      value = 1.0 / zero;
+	      value = INFINITY;
 	    }
 	  else if (cp[-1] == '+'
 		   && cp[0] == 'N' && cp[1] == 'a' && cp[2] == 'N')
 	    {
 	      state |= E_EXP;
 	      cp += 3;
-	      value = zero / zero;
-
-	      /* If that made a "negative" NaN, negate it.  */
-	      {
-		int i;
-		union { double d; char c[sizeof (double)]; }
-		  u_data, u_minus_zero;
-		u_data.d = value;
-		u_minus_zero.d = -0.0;
-		for (i = 0; i < sizeof (double); i++)
-		  if (u_data.c[i] & u_minus_zero.c[i])
-		    {
-		      value = -value;
-		      break;
-		    }
-	      }
-	      /* Now VALUE is a positive NaN.  */
+	      /* NAN is a "positive" NaN on all known Emacs hosts.  */
+	      value = NAN;
 	    }
 	  else
 	    cp = ecp;