libfortran: Provide fallback __issignalingl for IBM extended long double

On Mon, Jan 17, 2022 at 12:11:59AM +0100, FX via Gcc-patches wrote:
> This patch is the third in my “signaling NaN” series.
> For targets with IEEE support but without the issignaling macro in libc
> (i.e., everywhere except glibc), this allows us to provide a fallback
> implementation.

This doesn't seem to handle the powerpc* IBM double double long double.

__LDBL_IS_IEC_60559__ isn't defined for this type, because it is far from
an IEEE754 type, but it has signaling NaNs - as can be seen in glibc
libc/sysdeps/ieee754/ldbl-128ibm/s_issignalingl.c
the type is a pair of doubles and whether it is a sNaN or qNaN is determined
by whether the first double is a sNaN or qNaN.

2022-01-25  Jakub Jelinek  <jakub@redhat.com>

	* ieee/issignaling_fallback.h (__issignalingl): Define for
	IBM extended long double are returning __issignaling on the
	first double.

diff --git a/libgfortran/ieee/issignaling_fallback.h b/libgfortran/ieee/issignaling_fallback.h
index 4632bc5..5b9e1c8 100644 (file)
--- a/libgfortran/ieee/issignaling_fallback.h
+++ b/libgfortran/ieee/issignaling_fallback.h
@@ -137,6 +137,19 @@ __issignalingl (long double x)
   return ret || (((exi & 0x7fff) == 0x7fff) && (hxi > 0xc0000000));
 }
 
+#elif (__LDBL_DIG__ == 31)
+
+/* Long double is 128-bit IBM extended type.  */
+
+static inline int
+__issignalingl (long double x)
+{
+  union { long double value; double parts[2]; } u;
+
+  u.value = x;
+  return __issignaling (u.parts[0]);
+}
+
 #elif (__LDBL_DIG__ == 33) && __LDBL_IS_IEC_60559__
 
 /* Long double is 128-bit type.  */