math: support invalid ld80 representations in fpclassify

apparently gnulib requires invalid long double representations
to be handled correctly in printf so we classify them according
to how the fpu treats them: bad inf is nan, bad nan is nan,
bad normal is nan and bad subnormal/zero is minimal normal

diff --git a/src/math/__fpclassifyl.c b/src/math/__fpclassifyl.c
index 6365c58..6dc1002 100644 (file)
--- a/src/math/__fpclassifyl.c
+++ b/src/math/__fpclassifyl.c
@@ -3,13 +3,15 @@
 #if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
 
 #elif LDBL_MANT_DIG == 64 && LDBL_MAX_EXP == 16384
-/* invalid representations (top bit of u.i.m is wrong) are not handled */
 int __fpclassifyl(long double x)
 {
        union ldshape u = {x};
        int e = u.i.se & 0x7fff;
-       if (!e)
+       int msb = u.i.m>>63;
+       if (!e && !msb)
                return u.i.m ? FP_SUBNORMAL : FP_ZERO;
+       if (!msb)
+               return FP_NAN;
        if (e == 0x7fff)
                return u.i.m << 1 ? FP_NAN : FP_INFINITE;
        return FP_NORMAL;