Fix for problem reported by Neal Norwitz. Tighten up calculation of

slicelength.  Include his test case.

Lib/test/test_types.py

@@ -374,6 +374,8 @@ vereq(a[3::-2], [3,1])
 vereq(a[-100:100:], a)
 vereq(a[100:-100:-1], a[::-1])
 vereq(a[-100L:100L:2L], [0,2,4])
+vereq(a[1000:2000:2], [])
+vereq(a[-1000:-2000:-2], [])
 #  deletion
 del a[::2]
 vereq(a, [1,3])

Objects/sliceobject.c

@@ -152,12 +152,14 @@ PySlice_GetIndicesEx(PySliceObject *r, int length,
 		if (*stop > length) *stop = length;
 	}
 	
-	if (*step < 0) {
+	if ((*stop - *start)*(*step) <= 0) {
+		*slicelength = 0;
+	}
+	else if (*step < 0) {
 		*slicelength = (*stop-*start+1)/(*step)+1;
 	} else {
 		*slicelength = (*stop-*start-1)/(*step)+1;
 	}
-	if (*slicelength < 0) *slicelength = 0;
 
 	return 0;
 }