completed implementation

Author: flexatone

src/_arraykit.c

@@ -3337,7 +3337,7 @@ slice_to_ascending_slice(PyObject *Py_UNUSED(m), PyObject *args) {
         return NULL;
     }
 
-    Py_ssize_t len = -1;
+    Py_ssize_t step_count = -1;
     Py_ssize_t start = 0;
     Py_ssize_t stop = 0;
     Py_ssize_t step = 0;
@@ -3349,17 +3349,15 @@ slice_to_ascending_slice(PyObject *Py_UNUSED(m), PyObject *args) {
         Py_INCREF(slice);
         return slice;
     }
-    len = PySlice_AdjustIndices(
+    step_count = PySlice_AdjustIndices(
             PyLong_AsSsize_t(size),
             &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_stop = PyLong_FromSsize_t(start + 1);
-    PyObject* asc_start = PyLong_FromSsize_t(start + (step * (len - 1)));
+    // step will be negative; shift original start value down to find new start
+    PyObject* asc_start = PyLong_FromSsize_t(start + (step * (step_count - 1)));
     PyObject* asc_step = PyLong_FromSsize_t(-step);
 
     // might be NULL, let return

test/test_util.py

@@ -730,5 +730,20 @@ def test_slice_to_ascending_slice_d(self) -> None:
                 slice(4, 11, 2),
                 )
 
+    def test_slice_to_ascending_slice_e(self) -> None:
+        for slc, size in (
+                (slice(10, 2, -2), 12),
+                (slice(12, 2, -3), 12),
+                (slice(12, None, -4), 12),
+                (slice(76, 12, -8), 100),
+                (slice(81, 33, -12), 100),
+                (slice(97, 6, -7), 101),
+                ):
+            self.assertEqual(
+                slice_to_ascending_slice(slc, size),
+                slice_to_ascending_slice_ref(slc, size),
+                )
+
+
 if __name__ == '__main__':
     unittest.main()