Fix the construction of SimpleArray from slicing ndarray

cpp/modmesh/buffer/SimpleArray.hpp

@@ -32,6 +32,8 @@
 
 #include <limits>
 #include <stdexcept>
+#include <functional>
+#include <numeric>
 
 #if defined(_MSC_VER)
 #include <BaseTsd.h>
@@ -307,6 +309,65 @@ class SimpleArray
         }
     }
 
+    explicit SimpleArray(small_vector<size_t> const & shape,
+                         small_vector<size_t> const & stride,
+                         std::shared_ptr<buffer_type> const & buffer,
+                         bool is_c_contiguous = true,
+                         bool is_f_contiguous = false)
+        : SimpleArray(buffer)
+    {
+        if (buffer)
+        {
+            if (shape.size() != stride.size())
+            {
+                throw std::runtime_error("SimpleArray: shape and stride size mismatch");
+            }
+
+            if (is_c_contiguous)
+            {
+                if (stride[stride.size() - 1] != 1)
+                {
+                    throw std::runtime_error("SimpleArray: C contiguous stride must end with 1");
+                }
+                for (size_t it = 0; it < shape.size() - 1; ++it)
+                {
+                    if (stride[it] != shape[it + 1] * stride[it + 1])
+                    {
+                        throw std::runtime_error("SimpleArray: C contiguous stride must match shape");
+                    }
+                }
+            }
+            if (is_f_contiguous)
+            {
+                if (stride[0] != 1)
+                {
+                    throw std::runtime_error("SimpleArray: Fortran contiguous stride must start with 1");
+                }
+                for (size_t it = 0; it < shape.size() - 1; ++it)
+                {
+                    if (stride[it + 1] != shape[it] * stride[it])
+                    {
+                        throw std::runtime_error("SimpleArray: Fortran contiguous stride must match shape");
+                    }
+                }
+            }
+
+            const size_t nbytes = ITEMSIZE *
+                                  std::accumulate(shape.begin(),
+                                                  shape.end(),
+                                                  static_cast<size_t>(1),
+                                                  std::multiplies<size_t>());
+            if (nbytes != buffer->nbytes())
+            {
+                throw std::runtime_error(Formatter() << "SimpleArray: shape byte count " << nbytes
+                                                     << " differs from buffer " << buffer->nbytes());
+            }
+
+            m_shape = shape;
+            m_stride = stride;
+        }
+    }
+
     SimpleArray(std::initializer_list<T> init)
         : SimpleArray(init.size())
     {

cpp/modmesh/buffer/pymod/wrap_SimpleArray.cpp

@@ -74,16 +74,24 @@ class MODMESH_PYTHON_WRAPPER_VISIBILITY WrapSimpleArray
                         {
                             throw std::runtime_error("dtype mismatch");
                         }
+
                         modmesh::detail::shape_type shape;
+                        modmesh::detail::shape_type stride;
+                        constexpr size_t itemsize = wrapped_type::itemsize();
                         for (ssize_t i = 0; i < arr_in.ndim(); ++i)
                         {
                             shape.push_back(arr_in.shape(i));
+                            stride.push_back(arr_in.strides(i) / itemsize);
                         }
+
+                        const bool is_c_contiguous = (arr_in.flags() & py::array::c_style) == py::array::c_style;
+                        const bool is_f_contiguous = (arr_in.flags() & py::array::f_style) == py::array::f_style;
+
                         std::shared_ptr<ConcreteBuffer> const buffer = ConcreteBuffer::construct(
                             arr_in.nbytes(),
                             arr_in.mutable_data(),
                             std::make_unique<ConcreteBufferNdarrayRemover>(arr_in));
-                        return wrapped_type(shape, buffer);
+                        return wrapped_type(shape, stride, buffer, is_c_contiguous, is_f_contiguous);
                     }),
                 py::arg("array"))
             .def_buffer(&property_helper::get_buffer_info)

tests/test_buffer.py

@@ -450,6 +450,27 @@ def test_SimpleArray_from_ndarray_content(self):
         sarr.ndarray.fill(100)
         self.assertTrue((ndarr == 100).all())
 
+    def test_SimpleArray_from_ndarray_slice(self):
+        ndarr = np.arange(1000, dtype='float64').reshape((10, 10, 10))
+        parr = ndarr[1:7:3, 6:2:-1, 3:9]
+        sarr = modmesh.SimpleArrayFloat64(array=ndarr[1:7:3, 6:2:-1, 3:9])
+
+        for i in range(2):
+            for j in range(4):
+                for k in range(6):
+                    self.assertEqual(parr[i, j, k], sarr[i, j, k])
+
+    def test_SimpleArray_from_ndarray_transpose(self):
+        ndarr = np.arange(350, dtype='float64').reshape((5, 7, 10))
+        # The following array is F contiguous.
+        parr = ndarr[2:4].T
+        sarr = modmesh.SimpleArrayFloat64(array=ndarr[2:4].T)
+
+        for i in range(10):
+            for j in range(7):
+                for k in range(2):
+                    self.assertEqual(parr[i, j, k], sarr[i, j, k])
+
     def test_SimpleArray_broadcast_ellipsis_shape(self):
         sarr = modmesh.SimpleArrayFloat64((2, 3, 4))
         ndarr = np.arange(2 * 3 * 4, dtype='float64').reshape((2, 3, 4))