[FEA] Helpers for identifying contiguous layouts.

cpp/include/raft/core/mdspan.hpp

@@ -312,6 +312,41 @@ RAFT_INLINE_FUNCTION auto unravel_index(Idx idx,
 
 /** @} */
 
+/**
+ * @defgroup mdspan_contiguous Whether the strides imply a contiguous layout.
+ * @{
+ */
+
+/**
+ * @brief Whether the strides imply a c-contiguous layout.
+ */
+template <typename Extents, typename Strides>
+[[nodiscard]] auto is_c_contiguous(Extents const& extents, Strides const& strides) -> bool
+{
+  typename Extents::index_type stride = 1;
+  for (auto r = extents.rank(); r > 0; r--) {
+    if (stride != strides[r - 1]) { return false; }
+    stride *= extents.extent(r - 1);
+  }
+  return true;
+}
+
+/**
+ * @brief Whether the strides imply a f-contiguous layout.
+ */
+template <typename Extents, typename Strides>
+[[nodiscard]] auto is_f_contiguous(Extents const& extents, Strides const& strides) -> bool
+{
+  typename Extents::index_type stride = 1;
+  for (typename Extents::rank_type r = 0; r < extents.rank(); r++) {
+    if (stride != strides[r]) { return false; }
+    stride *= extents.extent(r);
+  }
+  return true;
+}
+
+/** @} */
+
 /**
  * @brief Const accessor specialization for default_accessor
  *

cpp/test/core/mdspan_utils.cu

@@ -247,4 +247,29 @@ void test_const_mdspan()
 
 TEST(MDSpan, ConstMDSpan) { test_const_mdspan(); }
 
+void test_contiguous_predicates()
+{
+  raft::resources handle;
+  extents<std::int64_t, dynamic_extent, dynamic_extent, dynamic_extent> exts{4, 4, 4};
+
+  {
+    std::array<std::int64_t, 3> strides{16, 4, 1};
+    ASSERT_TRUE(is_c_contiguous(exts, strides));
+    ASSERT_FALSE(is_f_contiguous(exts, strides));
+
+    // ensure that we are using the same stride unit (elements v.s. bytes) as mdarray
+    auto arr = make_host_mdarray<float>(handle, exts);
+    for (std::int32_t i = 0; i < 3; ++i) {
+      auto s = arr.stride(i);
+      ASSERT_EQ(s, strides[i]);
+    }
+  }
+  {
+    std::array<std::int64_t, 3> strides{1, 4, 16};
+    ASSERT_FALSE(is_c_contiguous(exts, strides));
+    ASSERT_TRUE(is_f_contiguous(exts, strides));
+  }
+}
+
+TEST(MDArray, Contiguous) { test_contiguous_predicates(); }
 }  // namespace raft

docs/source/conf.py

@@ -174,7 +174,7 @@
 # Example configuration for intersphinx: refer to the Python standard library.
 intersphinx_mapping = {
     "python": ("https://docs.python.org/", None),
-    "scipy": ("https://docs.scipy.org/doc/scipy/reference", None),
+    "scipy": ("https://docs.scipy.org/doc/scipy/", None),
 }
 
 # Config numpydoc

docs/source/cpp_api/mdspan_mdspan.rst

@@ -24,6 +24,11 @@ mdspan: Multi-dimensional Non-owning View
     :members:
     :content-only:
 
+.. doxygengroup:: mdspan_contiguous
+    :project: RAFT
+    :members:
+    :content-only:
+
 .. doxygengroup:: mdspan_make_const
     :project: RAFT
     :members: