isolate dpnp sua offset fix

onedal/datatypes/sycl_usm/data_conversion.cpp

@@ -86,8 +86,11 @@ dal::table convert_to_homogen_impl(py::object obj) {
     }
 
     // Get `__sycl_usm_array_interface__['data'][0]`, the first element of data entry,
-    // which is a Python integer encoding USM pointer value.
-    const auto* const ptr = reinterpret_cast<const Type*>(get_sua_ptr(sua_iface_dict));
+    // which is a Python integer encoding USM pointer value. The `offset` field (in
+    // elements) is applied because sliced views keep the base allocation pointer in
+    // `data[0]` and encode their start position via the offset instead.
+    const auto offset = get_sua_offset(sua_iface_dict);
+    const auto* const ptr = reinterpret_cast<const Type*>(get_sua_ptr(sua_iface_dict)) + offset;
 
     // Get SYCL object from `__sycl_usm_array_interface__["syclobj"]`.
     // syclobj: Python object from which SYCL context to which represented USM

onedal/datatypes/sycl_usm/sycl_usm_utils.cpp

@@ -89,6 +89,17 @@ bool is_sua_readonly(const py::dict& sua) {
     return data[1ul].cast<bool>();
 }
 
+// Get `__sycl_usm_array_interface__['offset']`, the offset in elements from the start
+// of the USM allocation to the first array element. The field is optional and defaults
+// to zero; sliced views (e.g. dpnp X[a:b]) report a non-zero offset while keeping the
+// same base pointer in `data[0]`, so it must be applied to avoid reading the wrong rows.
+std::int64_t get_sua_offset(const py::dict& sua) {
+    if (!sua.contains("offset") || sua["offset"].is_none()) {
+        return 0l;
+    }
+    return sua["offset"].cast<std::int64_t>();
+}
+
 // Get `__sycl_usm_array_interface__['shape']`.
 // shape : a tuple of integers describing dimensions of an N-dimensional array.
 py::tuple get_sua_shape(const py::dict& sua) {

onedal/datatypes/sycl_usm/sycl_usm_utils.hpp

@@ -42,6 +42,8 @@ std::uintptr_t get_sua_ptr(const py::dict& sua);
 
 bool is_sua_readonly(const py::dict& sua);
 
+std::int64_t get_sua_offset(const py::dict& sua);
+
 py::tuple get_sua_shape(const py::dict& sua);
 
 void report_problem_for_sua_iface(const char* clarification);

onedal/datatypes/tests/test_data.py

@@ -40,6 +40,7 @@
 from onedal.cluster.dbscan import DBSCAN
 from onedal.primitives import linear_kernel
 from onedal.tests.utils._dataframes_support import (
+    _as_numpy,
     _convert_to_dataframe,
     array_api_modules,
     get_dataframes_and_queues,
@@ -228,6 +229,43 @@ def test_input_zero_copy_sycl_usm(dataframe, queue, order, dtype):
     _assert_tensor_attr(X_dp, X_dp_from_table, order)
 
 
+@pytest.mark.skipif(
+    not dpctl_available,
+    reason="dpctl is required for checks.",
+)
+@pytest.mark.skipif(
+    not backend.is_dpc,
+    reason="__sycl_usm_array_interface__ support requires DPC backend.",
+)
+@pytest.mark.parametrize("dataframe,queue", get_dataframes_and_queues("dpnp", "cpu,gpu"))
+@pytest.mark.parametrize(
+    "slicer",
+    [
+        pytest.param(np.s_[3:], id="rows"),
+        pytest.param(np.s_[2:8], id="row_range"),
+        pytest.param(np.s_[::2], id="row_step"),
+        pytest.param(np.s_[:, 1:4], id="cols"),
+        pytest.param(np.s_[:, 2:3], id="single_col"),
+        pytest.param(np.s_[2:8, 1:4], id="row_and_col"),
+    ],
+)
+@pytest.mark.parametrize("dtype", [np.float32, np.float64])
+def test_sliced_view_offset_sycl_usm(dataframe, queue, slicer, dtype):
+    """A sliced view keeps the base allocation pointer in
+    `__sycl_usm_array_interface__['data'][0]` and encodes its start via the
+    `offset` field. The table conversion must apply that offset, otherwise the
+    view reads from row 0 (regression test for the SUA offset bug). Non-unit
+    steps and column subsets additionally exercise non-contiguous views.
+    """
+    X_np = np.arange(50, dtype=dtype).reshape(10, 5)
+    X_dp = _convert_to_dataframe(X_np, sycl_queue=queue, target_df=dataframe)
+
+    X_view = X_dp[slicer]
+    X_roundtrip = from_table(to_table(X_view), like=X_dp)
+
+    assert_allclose(_as_numpy(X_roundtrip), X_np[slicer])
+
+
 @pytest.mark.skipif(
     not dpctl_available,
     reason="dpctl is required for checks.",