From e28a37438d4ba71cd8a053e956686ab29ff97b6a Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@Penguin.CS.UCLA.EDU>
Date: Tue, 31 Jul 2018 23:46:57 -0700
Subject: [PATCH] Simplify by assuming C99 math.h isnan etc.

These should be portable nowadays.
* src/data.c (isnan): Remove.
* src/floatfns.c (isfinite, isnan): Remove.
* src/print.c: Include math.h, for isinf and isnan.
(float_to_string): Simplify by using them.
---
 src/data.c     |  4 ----
 src/floatfns.c |  7 -------
 src/print.c    | 20 ++++++--------------
 3 files changed, 6 insertions(+), 25 deletions(-)

diff --git a/src/data.c b/src/data.c
index c8beeda7208..aaccb675183 100644
--- a/src/data.c
+++ b/src/data.c
@@ -2812,10 +2812,6 @@ arith_driver (enum arithop code, ptrdiff_t nargs, Lisp_Object *args)
   return val;
 }
 
-#ifndef isnan
-# define isnan(x) ((x) != (x))
-#endif
-
 static Lisp_Object
 float_arith_driver (double accum, ptrdiff_t argnum, enum arithop code,
 		    ptrdiff_t nargs, Lisp_Object *args)
diff --git a/src/floatfns.c b/src/floatfns.c
index e7d404a84e0..45e786f9669 100644
--- a/src/floatfns.c
+++ b/src/floatfns.c
@@ -47,13 +47,6 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 
 #include <count-leading-zeros.h>
 
-#ifndef isfinite
-# define isfinite(x) ((x) - (x) == 0)
-#endif
-#ifndef isnan
-# define isnan(x) ((x) != (x))
-#endif
-
 /* Check that X is a floating point number.  */
 
 static void
diff --git a/src/print.c b/src/print.c
index 71591952a23..da6ec1aaedf 100644
--- a/src/print.c
+++ b/src/print.c
@@ -38,6 +38,7 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 #include <c-ctype.h>
 #include <float.h>
 #include <ftoastr.h>
+#include <math.h>
 
 #ifdef WINDOWSNT
 # include <sys/socket.h> /* for F_DUPFD_CLOEXEC */
@@ -1001,23 +1002,14 @@ float_to_string (char *buf, double data)
   int width;
   int len;
 
-  /* Check for plus infinity in a way that won't lose
-     if there is no plus infinity.  */
-  if (data == data / 2 && data > 1.0)
-    {
-      static char const infinity_string[] = "1.0e+INF";
-      strcpy (buf, infinity_string);
-      return sizeof infinity_string - 1;
-    }
-  /* Likewise for minus infinity.  */
-  if (data == data / 2 && data < -1.0)
+  if (isinf (data))
     {
       static char const minus_infinity_string[] = "-1.0e+INF";
-      strcpy (buf, minus_infinity_string);
-      return sizeof minus_infinity_string - 1;
+      bool positive = 0 < data;
+      strcpy (buf, minus_infinity_string + positive);
+      return sizeof minus_infinity_string - 1 - positive;
     }
-  /* Check for NaN in a way that won't fail if there are no NaNs.  */
-  if (! (data * 0.0 >= 0.0))
+  if (isnan (data))
     {
       /* Prepend "-" if the NaN's sign bit is negative.
 	 The sign bit of a double is the bit that is 1 in -0.0.  */
-- 
2.39.2