infnan: the nan quiet/signaling bit is not enough

1 files changed, 32 insertions, 0 deletions

diff --git a/perl.h b/perl.h
index cfbadefd6c..b4ac7f5621 100644
--- a/perl.h
+++ b/perl.h
@@ -4363,6 +4363,38 @@ static const union { unsigned int __i; float __f; } __PL_nan_u =
  * Though IEEE-754-logically correct, some compilers (like Visual C 2003)
  * falsely misoptimize that to zero (x-x is zero, right?) */
 
+/* x86 80-bit extended precision mantissa bits:
+ *
+ * 63 62 61   30387+    pre-387
+ * --------   ----      --------
+ *  0  0  0   invalid   infinity
+ *  0  0  n   invalid   snan
+ *  0  1  *   invalid   snan
+ *  1  0  0   infinity  snan
+ *  1  0  n   snan
+ *  1  1  0   qnan (1.#IND)
+ *  1  1  n   qnan
+ *
+ * This means that there are 61 bits for nan payload.
+ */
+#if defined(USE_LONG_DOUBLE) && (LONG_DOUBLEKIND == LONG_DOUBLE_IS_X86_80_BIT_LITTLE_ENDIAN)
+#  define NV_NAN_BITS 61
+#elif defined(__hppa) /* XXX Configure scan */
+#  define NV_NAN_BITS 50 /* qnan: 7f f4 00 00 00 00 00 00 */
+#elif defined(__mips) && UVSIZE == 4 /* IRIX64/MIPS cc -32 */
+#  define NV_NAN_BITS 35 /* qnan: 7f ff 2f 30 00 00 00 00
+                          * +inf: 7f ff 2f 20 00 00 00 00
+                          * -inf: 7f ff 2f 28 00 00 00 00 */
+#else
+#  define NV_NAN_BITS (NV_MANT_REAL_DIG - 1)
+#endif
+/* IRIX64/MIPS cc -64 is something bizarre:
+ * qnan 00 00 0f ff ff ff ae 90
+ * +inf 00 00 0f ff ff ff ae 80
+ * -inf 00 00 0f ff ff ff ae 88
+ * In other words, it doesn't seem to follow any IEEE pattern for infnan,
+ * and even seems more little-endian than big-endian. */
+
 #ifndef __cplusplus
 #  if !defined(WIN32) && !defined(VMS)
 #ifndef crypt