Indexing bug (#233)

* fix

* test

python/src/indexing.cpp

@@ -120,6 +120,11 @@ array mlx_gather_nd(
     if (py::isinstance<py::slice>(idx)) {
       int start, end, stride;
       get_slice_params(start, end, stride, idx, src.shape(i));
+
+      // Handle negative indices
+      start = (start < 0) ? start + src.shape(i) : start;
+      end = (end < 0) ? end + src.shape(i) : end;
+
       gather_indices.push_back(arange(start, end, stride, uint32));
       num_slices++;
       is_slice[i] = true;

python/tests/test_array.py

@@ -727,6 +727,11 @@ class TestArray(mlx_tests.MLXTestCase):
             np.array_equal(a_np[idx_np, idx_np], np.array(a_mlx[idx_mlx, idx_mlx]))
         )
 
+        # Slicing with negative indices and integer
+        a_np = np.arange(10).reshape(5, 2)
+        a_mlx = mx.array(a_np)
+        self.assertTrue(np.array_equal(a_np[2:-1, 0], np.array(a_mlx[2:-1, 0])))
+
     def test_setitem(self):
         a = mx.array(0)
         a[None] = 1