Some days, I think my comment of

	/* this is harder to get right than you might think */

angered some God somewhere.  After noticing

    >>> range(5000000)[slice(96360, None, 439)]
    []

I found that my cute test for the slice being empty failed due to
overflow.  Fixed, and added simple test (not the above!).

1 files changed, 12 insertions, 6 deletions

diff --git a/Objects/sliceobject.c b/Objects/sliceobject.c
index 21426a7..a035e5f 100644
--- a/Objects/sliceobject.c
+++ b/Objects/sliceobject.c
@@ -114,11 +114,13 @@ PySlice_GetIndicesEx(PySliceObject *r, int length,
 		     int *start, int *stop, int *step, int *slicelength)
 {
 	/* this is harder to get right than you might think */
+
 	int defstart, defstop;
 
 	if (r->step == Py_None) {
 		*step = 1;
-	} else {
+	} 
+	else {
 		*step = PyInt_AsLong(r->step);
 		if (*step == -1 && PyErr_Occurred()) {
 			return -1;
@@ -135,7 +137,8 @@ PySlice_GetIndicesEx(PySliceObject *r, int length,
 
 	if (r->start == Py_None) {
 		*start = defstart;
-	} else {
+	}
+	else {
 		if (!_PyEval_SliceIndex(r->start, start)) return -1;
 		if (*start < 0) *start += length;
 		if (*start < 0) *start = (*step < 0) ? -1 : 0;
@@ -145,19 +148,22 @@ PySlice_GetIndicesEx(PySliceObject *r, int length,
 
 	if (r->stop == Py_None) {
 		*stop = defstop;
-	} else {
+	}
+	else {
 		if (!_PyEval_SliceIndex(r->stop, stop)) return -1;
 		if (*stop < 0) *stop += length;
 		if (*stop < 0) *stop = -1;
 		if (*stop > length) *stop = length;
 	}
-	
-	if ((*stop - *start)*(*step) <= 0) {
+
+	if ((*step < 0 && *stop >= *start) 
+	    || (*step > 0 && *start >= *stop)) {
 		*slicelength = 0;
 	}
 	else if (*step < 0) {
 		*slicelength = (*stop-*start+1)/(*step)+1;
-	} else {
+	}
+	else {
 		*slicelength = (*stop-*start-1)/(*step)+1;
 	}