Re: QNaN and SNaN definitions

[Hartvig Ekner <hartvige at mips dot com>]

H . J . Lu writes:
> 
> On Tue, Mar 19, 2002 at 10:34:11PM +0100, Hartvig Ekner wrote:
> > < stuff on NaN>
> >
> > I can send in patches to fix this for MIPS, but I would think this is
> > inappropriate and that some of you glibc people would have to decide how
> > to deal with this. If you can tell me how you want it fixed, I will be
> > happy to deliver the patches, but I need a machine specific #define to
> > look at in these header files. I would like to avoid separate MIPS versions
> > of these header files if possible (maintenance issues).
> 
> Just create a new sysdeps/mips/bits/nan.h with the right bits.
> 
> > 
> > In nan.h, it is clear what has to be done. 
> > 
> > In ieee754.h it is less clear. One can leave things as they are, but then
> > peoples apps will not work without them knowing the difference. Maybe define
> > machine-dep constants to be used with the quiet_nan field, or more 
> > drastically, rename the quiet_nan field to signalling_nan. Is this an
> > option at all?
> > 
> 
> You can create a new sysdeps/mips/ieee754.h and change quiet_nan to
> signalling_nan. Any codes depending on quiet_nan will fail on mips

I would really like to avoid especially ieee754 branching off into a 
separate MIPS file, since it contains a lot of other stuff than the
quiet_nan thing.

How about these two patches to the generic files in sysdeps?

/Hartvig



===================================================================
RCS file: RCS/nan.h,v
retrieving revision 1.1
diff -u -r1.1 nan.h
--- nan.h	2002/03/20 20:43:26	1.1
+++ nan.h	2002/03/20 20:57:56
@@ -22,24 +22,42 @@
 #endif
 
 
-/* IEEE Not A Number.  */
+/* IEEE Not A Number. Note that MIPS has the QNaN and SNaN patterns 
+   reversed compared to most other architectures. The IEEE spec left
+   the definition of this open to implementations, and for MIPS the top
+   bit of the mantissa must be SET to indicate a SNaN.  */
 
 #ifdef	__GNUC__
 
+# ifdef __mips__
+#  define QNAN_PATTERN	0x7fbfffffUL
+# else
+#  define QNAN_PATTERN	0x7fc00000UL
+# endif
+
 # define NAN \
   (__extension__                                                            \
    ((union { unsigned __l __attribute__((__mode__(__SI__))); float __d; })  \
-    { __l: 0x7fc00000UL }).__d)
+    { __l: QNAN_PATTERN }).__d)
 
 #else
 
 # include <endian.h>
 
 # if __BYTE_ORDER == __BIG_ENDIAN
-#  define __nan_bytes		{ 0x7f, 0xc0, 0, 0 }
+#  ifdef __mips__
+#   define __nan_bytes		{ 0x7f, 0xbf, 0xff, 0xff }
+#  else
+#   define __nan_bytes		{ 0x7f, 0xc0, 0x00, 0x00 }
+#  endif
 # endif
+
 # if __BYTE_ORDER == __LITTLE_ENDIAN
-#  define __nan_bytes		{ 0, 0, 0xc0, 0x7f }
+#  ifdef __mips__
+#   define __nan_bytes		{ 0xff, 0xff, 0xbf, 0x7f }
+#  else
+#   define __nan_bytes		{ 0x00, 0x00, 0xc0, 0x7f }
+#  endif
 # endif
 
 static union { unsigned char __c[4]; float __d; } __nan_union = { __nan_bytes };
===================================================================
RCS file: RCS/ieee754.h,v
retrieving revision 1.1
diff -u -r1.1 ieee754.h
--- ieee754.h	2002/03/20 20:43:26	1.1
+++ ieee754.h	2002/03/20 21:12:01
@@ -25,6 +25,21 @@
 
 __BEGIN_DECLS
 
+/* Note that MIPS has the QNaN and SNaN patterns reversed compared to
+   most other architectures. See bits/nan.h for more detail.
+
+   The constants below can be used to portably manipulate the "quiet_nan"
+   bitfields in the IEEE754 unions, which for MIPS should actually be named
+   "signalling_nan".  */
+
+#ifdef	__mips__
+# define IEEE754_QNAN_BIT	0
+# define IEEE754_SNAN_BIT	1
+#else
+# define IEEE754_QNAN_BIT	1
+# define IEEE754_SNAN_BIT	0
+#endif
+
 union ieee754_float
   {
     float f;