Merge pull request #5086 from mdboom/stride-fix

Fix how strides is set on Py_buffer object when the array is C-contiguous

2 files changed, 54 insertions, 2 deletions

diff --git a/numpy/core/src/multiarray/buffer.c b/numpy/core/src/multiarray/buffer.c
index 6ba98d1cd..7f7607e1f 100644
--- a/numpy/core/src/multiarray/buffer.c
+++ b/numpy/core/src/multiarray/buffer.c
@@ -629,6 +629,8 @@ array_getbuffer(PyObject *obj, Py_buffer *view, int flags)
 {
     PyArrayObject *self;
     _buffer_info_t *info = NULL;
+    int i;
+    Py_ssize_t sd;
 
     self = (PyArrayObject*)obj;
 
@@ -703,6 +705,31 @@ array_getbuffer(PyObject *obj, Py_buffer *view, int flags)
     }
     if ((flags & PyBUF_STRIDES) == PyBUF_STRIDES) {
         view->strides = info->strides;
+
+#ifdef NPY_RELAXED_STRIDES_CHECKING
+        /*
+         * If NPY_RELAXED_STRIDES_CHECKING is on, the array may be
+         * contiguous, but it won't look that way to Python when it
+         * tries to determine contiguity by looking at the strides
+         * (since one of the elements may be -1).  In that case, just
+         * regenerate strides from shape.
+         */
+        if (PyArray_CHKFLAGS(self, NPY_ARRAY_C_CONTIGUOUS) &&
+            !((flags & PyBUF_F_CONTIGUOUS) == PyBUF_F_CONTIGUOUS)) {
+            sd = view->itemsize;
+            for (i = view->ndim-1; i >= 0; --i) {
+                view->strides[i] = sd;
+                sd *= view->shape[i];
+            }
+        }
+        else if (PyArray_CHKFLAGS(self, NPY_ARRAY_F_CONTIGUOUS)) {
+            sd = view->itemsize;
+            for (i = 0; i < view->ndim; ++i) {
+                view->strides[i] = sd;
+                sd *= view->shape[i];
+            }
+        }
+#endif
     }
     else {
         view->strides = NULL;
@@ -922,7 +949,7 @@ _descriptor_from_pep3118_format_fast(char *s, PyObject **result)
         *result = (PyObject*)PyArray_DescrNewByteorder(descr, byte_order);
         Py_DECREF(descr);
     }
-    
+
     return 1;
 }
 
diff --git a/numpy/core/tests/test_multiarray.py b/numpy/core/tests/test_multiarray.py
index 6cbe36f03..d6f98e0b7 100644
--- a/numpy/core/tests/test_multiarray.py
+++ b/numpy/core/tests/test_multiarray.py
@@ -1921,7 +1921,7 @@ class TestMethods(TestCase):
 
         a = np.array([1-1j, 1, 2.0, 'f'], object)
         assert_raises(AttributeError, lambda: a.conj())
-        assert_raises(AttributeError, lambda: a.conjugate()) 
+        assert_raises(AttributeError, lambda: a.conjugate())
 
 
 class TestBinop(object):
@@ -4316,6 +4316,31 @@ class TestNewBufferProtocol(object):
         x3 = np.arange(dt3.itemsize, dtype=np.int8).view(dt3)
         self._check_roundtrip(x3)
 
+    def test_relaxed_strides(self):
+        # Test that relaxed strides are converted to non-relaxed
+        c = np.ones((1, 10, 10), dtype='i8')
+
+        # Check for NPY_RELAXED_STRIDES_CHECKING:
+        if np.ones((10, 1), order="C").flags.f_contiguous:
+            c.strides = (-1, 80, 8)
+
+        assert memoryview(c).strides == (800, 80, 8)
+
+        # Writing C-contiguous data to a BytesIO buffer should work
+        fd = io.BytesIO()
+        fd.write(c.data)
+
+        fortran = c.T
+        assert memoryview(fortran).strides == (8, 80, 800)
+
+        arr = np.ones((1, 10))
+        if arr.flags.f_contiguous:
+            shape, strides = get_buffer_info(arr, ['F_CONTIGUOUS'])
+            assert_(strides[0] == 8)
+            arr = np.ones((10, 1), order='F')
+            shape, strides = get_buffer_info(arr, ['C_CONTIGUOUS'])
+            assert_(strides[-1] == 8)
+
 
 class TestArrayAttributeDeletion(object):