progress

Author: flexatone

src/_arraykit.c

@@ -3354,9 +3354,12 @@ slice_to_ascending_slice(PyObject *Py_UNUSED(m), PyObject *args) {
             &start,
             &stop,
             step);
+    // AK_DEBUG_MSG_OBJ("resolved slice", Py_BuildValue("nnnn", pos, stop, step, len));
+
+    // real stop is (len-1); len is negative
 
-    PyObject* asc_start = PyLong_FromSsize_t(stop + 1);
     PyObject* asc_stop = PyLong_FromSsize_t(start + 1);
+    PyObject* asc_start = PyLong_FromSsize_t(start + (step * (len - 1)));
     PyObject* asc_step = PyLong_FromSsize_t(-step);
 
     // might be NULL, let return

test/test_util.py

@@ -724,7 +724,11 @@ def test_slice_to_ascending_slice_c(self) -> None:
         with self.assertRaises(TypeError):
             _ = slice_to_ascending_slice(slice(1, 4), 'x')
 
-
+    def test_slice_to_ascending_slice_d(self) -> None:
+        self.assertEqual(slice_to_ascending_slice(
+                slice(10, 2, -2), 12),
+                slice(4, 11, 2),
+                )
 
 if __name__ == '__main__':
     unittest.main()