Fix downward slices for positive base arrays

Author: BCSharp

Src/IronPython/Runtime/Operations/ArrayOps.cs

@@ -495,7 +495,7 @@ private static void FixSlice(Slice slice, Array a, out int ostart, out int ostop
                     if (ostop < 0 && lb >= 0) {
                         ostop += ub + 1;
                     }
-                    if (ostop < 0) {
+                    if (ostop < lb) {
                         ostop = ostep > 0 ? lb : lb - 1;
                     }
                 } else if (ostop > ub) {

Tests/test_array.py

@@ -497,4 +497,20 @@ def test_equality_rank(self):
         self.assertTrue(c != d)
         self.assertFalse(d != d1)
 
+    def test_slice_down(self):
+        #arr = System.Array[int]((2, 3, 4), base=2)
+        arr = System.Array.CreateInstance(int, (3,), (2,))
+        for i in range(2, 2 + 3):
+            arr[i] = i
+
+        self.assertEqual(arr[-1:-4:-1], System.Array[int]((4, 3, 2)))
+        self.assertEqual(arr[-1:-5:-1], System.Array[int]((4, 3, 2)))
+        self.assertEqual(arr[-1:-6:-1], System.Array[int]((4, 3, 2)))
+
+        self.assertEqual(arr[2:1:-1], System.Array[int]((2,)))
+        self.assertEqual(arr[2:-5:-1], System.Array[int]((2,)))
+        self.assertEqual(arr[2:-6:-1], System.Array[int]((2,)))
+        self.assertEqual(arr[1:-5:-1], System.Array[int](()))
+        self.assertEqual(arr[0:-5:-1], System.Array[int](()))
+
 run_test(__name__)