Use memoryview for constructing array from buffer

include/pybind11/numpy.h

@@ -13,6 +13,7 @@
 #include "complex.h"
 #include <numeric>
 #include <algorithm>
+#include <cstdlib>
 
 #if defined(_MSC_VER)
 #pragma warning(push)
@@ -31,6 +32,7 @@ public:
             API_PyArray_FromAny = 69,
             API_PyArray_NewCopy = 85,
             API_PyArray_NewFromDescr = 94,
+            API_PyArray_GetArrayParamsFromObject = 278,
 
             NPY_C_CONTIGUOUS_ = 0x0001,
             NPY_F_CONTIGUOUS_ = 0x0002,
@@ -61,6 +63,7 @@ public:
             DECL_NPY_API(PyArray_FromAny);
             DECL_NPY_API(PyArray_NewCopy);
             DECL_NPY_API(PyArray_NewFromDescr);
+            DECL_NPY_API(PyArray_GetArrayParamsFromObject);
 #undef DECL_NPY_API
             return api;
         }
@@ -74,6 +77,8 @@ public:
         PyObject *(*PyArray_NewCopy_)(PyObject *, int);
         PyTypeObject *PyArray_Type_;
         PyObject *(*PyArray_FromAny_) (PyObject *, PyObject *, int, int, int, PyObject *);
+        int (*PyArray_GetArrayParamsFromObject_)(PyObject *, PyObject *, char, PyObject **, int *,
+                                                 Py_ssize_t *, PyObject **, PyObject *);
     };
 
     PYBIND11_OBJECT_DEFAULT(array, buffer, lookup_api().PyArray_Check_)
@@ -100,24 +105,22 @@ public:
     }
 
     array(const buffer_info &info) {
-        API& api = lookup_api();
-        if ((info.format.size() < 1) || (info.format.size() > 2))
-            pybind11_fail("Unsupported buffer format!");
-        int fmt = (int) info.format[0];
-        if (info.format == "Zd")      fmt = API::NPY_CDOUBLE_;
-        else if (info.format == "Zf") fmt = API::NPY_CFLOAT_;
+        PyObject *arr = nullptr, *descr = nullptr;
+        int ndim = 0;
+        Py_ssize_t dims[32];
 
-        PyObject *descr = api.PyArray_DescrFromType_(fmt);
-        if (descr == nullptr)
-            pybind11_fail("NumPy: unsupported buffer format '" + info.format + "'!");
-        object tmp(api.PyArray_NewFromDescr_(
-            api.PyArray_Type_, descr, (int) info.ndim, (Py_intptr_t *) &info.shape[0],
-            (Py_intptr_t *) &info.strides[0], info.ptr, 0, nullptr), false);
-        if (info.ptr && tmp)
-            tmp = object(api.PyArray_NewCopy_(tmp.ptr(), -1 /* any order */), false);
-        if (!tmp)
-            pybind11_fail("NumPy: unable to create array!");
-        m_ptr = tmp.release().ptr();
+        // allocate zeroed memory if it hasn't been provided
+        auto buf_info = info;
+        if (!buf_info.ptr)
+            buf_info.ptr = std::calloc(info.size, info.itemsize);
+        auto view = py::memoryview(buf_info);
+
+        API& api = lookup_api();
+        auto res = api.PyArray_GetArrayParamsFromObject_(view.ptr(), nullptr, 1, &descr,
+                                                         &ndim, dims, &arr, nullptr);
+        if (res < 0 || !arr || descr)
+            pybind11_fail("NumPy: unable to convert buffer to an array");
+        m_ptr = arr;
     }
 
 protected: