Use a more robust infinity check in _Py_HashDouble.

This fixes a test_decimal failure on FreeBSD 8.0.  (modf apparently
doesn't follow C99 Annex F on FreeBSD.)

Lib/test/test_float.py

@@ -948,6 +948,15 @@ class InfNanTest(unittest.TestCase):
         self.assertFalse(NAN.is_inf())
         self.assertFalse((0.).is_inf())
 
+    def test_hash_inf(self):
+        # the actual values here should be regarded as an
+        # implementation detail, but they need to be
+        # identical to those used in the Decimal module.
+        self.assertEqual(hash(float('inf')), 314159)
+        self.assertEqual(hash(float('-inf')), -271828)
+        self.assertEqual(hash(float('nan')), 0)
+
+
 fromHex = float.fromhex
 toHex = float.hex
 class HexFloatTestCase(unittest.TestCase):

Objects/object.c

@@ -1025,15 +1025,15 @@ _Py_HashDouble(double v)
 	 * of mapping keys will turn out weird.
 	 */
 
+	if (Py_IS_INFINITY(v))
+		/* can't convert to long int -- arbitrary */
+		v = v < 0 ? -271828.0 : 314159.0;
 	fractpart = modf(v, &intpart);
 	if (fractpart == 0.0) {
 		/* This must return the same hash as an equal int or long. */
 		if (intpart > LONG_MAX/2 || -intpart > LONG_MAX/2) {
 			/* Convert to long and use its hash. */
 			PyObject *plong;	/* converted to Python long */
-			if (Py_IS_INFINITY(intpart))
-				/* can't convert to long int -- arbitrary */
-				v = v < 0 ? -271828.0 : 314159.0;
 			plong = PyLong_FromDouble(v);
 			if (plong == NULL)
 				return -1;