From bug-request at octave dot org Fri Dec 17 09:05:29 2004
Subject: Re: signbit on linux/gcc 3.2+
From: "John W. Eaton" <jwe at bevo dot che dot wisc dot edu>
To: Orion Poplawski <orion at cora dot nwra dot com>
Cc: bug at octave dot org
Date: Fri, 17 Dec 2004 10:06:06 -0500

On 16-Dec-2004, Orion Poplawski <orion at cora dot nwra dot com> wrote:

| --- octave-2.1.64/configure.in.orig     2004-11-11 22:40:15.000000000 -0700
| +++ octave-2.1.64/configure.in  2004-12-16 16:34:16.209266151 -0700
|  at @ -1153,6 +1153,7 @@
|     ;;
|     *)
|       AC_CHECK_FUNCS(finite isnan isinf copysign signbit)
| +    AC_CHECK_DECLS(signbit,,,[#include <math.h>])
|     ;;
|   esac

This is OK, so I've included it.

| --- octave-2.1.64/liboctave/lo-ieee.h.orig      2003-09-05 
| 10:55:42.000000000 -0600
| +++ octave-2.1.64/liboctave/lo-ieee.h   2004-12-16 16:34:01.509814447 -0700
|  at @ -24,6 +24,13 @@
|   #define octave_liboctave_ieee_h 1
| 
| +/* Use c++ signbit */
| +#include <cmath>
| +/* GNUC puts it in std:: */
| +#ifdef __GNUC__
| +using std::signbit;
| +#endif
| +

This won't work because lo-ieee.h is included by lo-cieee.c, which is
not C++.

Also, I'd rather not assume we know that GCC will always put signbit
in the std namespace, since that seems like it could change (is it
supposed to be in std?) in some future version and may not even be
true for some older versions of GCC that are still used to compile
Octave.

I thought the following change would be good

liboctave/ChangeLog:

2004-12-17  John W. Eaton  <jwe at octave dot org>

	* lo-cieee.c (lo_ieee_signbit): New function.
	* lo-ieee.h: Provide decl.
	Don't define lo_ieee_signbit as a macro here.
	From Orion Poplawski <orion at cora dot nwra dot com>.
 

Index: lo-cieee.c
===================================================================
RCS file: /usr/local/cvsroot/octave/liboctave/lo-cieee.c,v
retrieving revision 1.6
diff -u -r1.6 lo-cieee.c
--- lo-cieee.c	5 Sep 2003 16:55:42 -0000	1.6
+++ lo-cieee.c	17 Dec 2004 14:56:56 -0000
 at @ -153,6 +153,30 @@
   return octave_NaN;
 }
 
+#if ! (defined (signbit) || defined (HAVE_DECL_SIGNBIT)) && defined (HAVE_SIGNBIT)
+extern int signbit (double);
+#endif
+
+int
+lo_ieee_signbit (double x)
+{
+/* In the following definitions, only check x < 0 explicitly to avoid
+   a function call when it looks like signbit or copysign are actually
+   functions.  */
+
+#if defined (signbit)
+  return signbit (x);
+#elif defined (HAVE_SIGNBIT)
+  return (x < 0 || signbit (x));
+#elif defined (copysign)
+  return (copysign (1.0, x) < 0);
+#elif defined (HAVE_COPYSIGN)
+  return (x < 0 || copysign (1.0, x) < 0);
+#else
+  return x < 0;
+#endif
+}
+
 /*
 ;;; Local Variables: ***
 ;;; mode: C++ ***
Index: lo-ieee.h
===================================================================
RCS file: /usr/local/cvsroot/octave/liboctave/lo-ieee.h,v
retrieving revision 1.13
diff -u -r1.13 lo-ieee.h
--- lo-ieee.h	5 Sep 2003 16:55:42 -0000	1.13
+++ lo-ieee.h	17 Dec 2004 14:56:56 -0000
 at @ -66,24 +66,7 @@
 extern double lo_ieee_na_value (void);
 extern double lo_ieee_nan_value (void);
 
-/* In the following definitions, only check x < 0 explicitly to avoid
-   a function call when it looks like signbit or copysign are actually
-   functions.  */
-
-#if defined (signbit)
-#define lo_ieee_signbit(x) signbit (x)
-#elif defined (HAVE_SIGNBIT)
-#if defined (__MINGW32__)
-extern int signbit (double);
-#endif
-#define lo_ieee_signbit(x) (x < 0 || signbit (x))
-#elif defined (copysign)
-#define lo_ieee_signbit(x) (copysign (1.0, x) < 0)
-#elif defined (HAVE_COPYSIGN)
-#define lo_ieee_signbit(x) (x < 0 || copysign (1.0, x) < 0)
-#else
-#define lo_ieee_signbit(x) 0
-#endif
+extern int lo_ieee_signbit (double);
 
 #ifdef	__cplusplus
 }


and it will work, but on my system (Debian, GCC 3.3.4) it will use the

  return (x < 0 || copysign (1.0, x) < 0);

version, because signbit is only defined in math.h when the compiler
is in C99 mode.  Do we want to try to enable that (I'd guess not yet)
or should we just check for __signbit in the configure script?

jwe



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