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ENH: Add support for PEP 3118 buffers with offsets (non-contiguous) #7467

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ENH: Add support for PEP 3118 buffers with offsets (non-contiguous) #7467

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247dc33
BUG: Fixes issue #5412.
abalkin Jan 2, 2015
ec9e11a
FIX: PyArray_NewFromDescr steals descr, no need to set base since dat…
abalkin Mar 27, 2016
76689cf
FIX: Initialize last_axis to make compiler happy.
abalkin Mar 28, 2016
730aa71
FIX: Added a comment explaining initialization for last_axis.
abalkin Mar 28, 2016
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91 changes: 81 additions & 10 deletions numpy/core/src/multiarray/ctors.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1259,6 +1259,57 @@ PyArray_New(PyTypeObject *subtype, int nd, npy_intp *dims, int type_num,
return new;
}

int
_copy_from_pil_style(char* dest, int ndim, char *buf, npy_intp *shape,
npy_intp *strides, npy_intp *suboffsets, npy_intp itemsize)
{
npy_intp indices[NPY_MAXDIMS];
void **pointers[NPY_MAXDIMS];
char *pointer = (char*)buf;
npy_intp blocksize;
int ax;
/* Since suboffsets cannot be all negative, last_axis will be inevitably
* reset in the initialization loop below. However, the compiler cannot
* know this, so we preset last_axis to an arbitrary value. */
int last_axis = 0;

/* Initialize indices and pointers. */
for (ax = 0; ax < ndim; ++ax) {
indices[ax] = 0;
pointers[ax] = (void **)pointer;
if (suboffsets[ax] >= 0) {
last_axis = ax;
pointer = *((char**)pointer) + suboffsets[ax];
}
}
/* compute blocksize */
blocksize = itemsize;
for (ax = last_axis + 1; ax < ndim; ++ax)
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If all suboffsets[ax] < 0 then last_axis never gets initialized when we get here. Even if that is not really possible (is it not?) the compiler does not seem able to figure it out, and that's what's making Travis unhappy. I guess the right value to initialize it at the beginning of the function is -1?

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suboffsets cannot be all negative because this would mean no dereferencing and the PEP requires that suboffsets pointer be NULL in this case. If not for that requirement, the right initial value would indeed be -1, but I don't want to introduce confusion between real -1 and -1 that means ndim - 1, so I just initialize last_axis to 0.

blocksize *= shape[ax];
/* main loop */
for (;;) {
memcpy(dest, pointer, blocksize);
dest += blocksize;
ax = last_axis;
/* Update indices and pointers for the next block. */
while (indices[ax] == shape[ax] - 1) {
if (ax == 0)
return 0;
indices[ax--] = 0;
}
++indices[ax];
/* update pointers */
pointer = (char *)pointers[ax] + strides[ax];
for (; ax <= last_axis; ++ax) {
pointers[ax] = (void **)pointer;
if (suboffsets[ax] >=0 ) {
pointer = *((char**)pointer) + suboffsets[ax];
}
}
}
return -1;
}


NPY_NO_EXPORT int
_array_from_buffer_3118(PyObject *obj, PyObject **out)
Expand Down Expand Up @@ -1344,23 +1395,43 @@ _array_from_buffer_3118(PyObject *obj, PyObject **out)
}
}

flags = NPY_ARRAY_BEHAVED & (view->readonly ? ~NPY_ARRAY_WRITEABLE : ~0);
r = PyArray_NewFromDescr(&PyArray_Type, descr,
nd, shape, strides, view->buf,
flags, NULL);
if (r == NULL ||
PyArray_SetBaseObject((PyArrayObject *)r, memoryview) < 0) {
Py_XDECREF(r);
Py_DECREF(memoryview);
return -1;
if (view->suboffsets == NULL) {
flags = NPY_ARRAY_BEHAVED & (view->readonly ? ~NPY_ARRAY_WRITEABLE : ~0);
r = PyArray_NewFromDescr(&PyArray_Type, descr,
nd, shape, strides, view->buf,
flags, NULL);
if (r == NULL ||
PyArray_SetBaseObject((PyArrayObject *)r, memoryview) < 0) {
Py_XDECREF(r);
Py_DECREF(memoryview);
return -1;
}
PyArray_UpdateFlags((PyArrayObject *)r, NPY_ARRAY_UPDATE_ALL);
}
PyArray_UpdateFlags((PyArrayObject *)r, NPY_ARRAY_UPDATE_ALL);
else {
/* Recompute strides */
npy_intp blocksize = view->itemsize;
for (k = nd - 1; k >= 0; --k) {
if (view->suboffsets[k] >= 0) {
strides[k] = blocksize;
}
blocksize *= shape[k];
}
r = PyArray_NewFromDescr(&PyArray_Type, descr,
nd, shape, strides, NULL, 0, NULL);
if (r == NULL)
goto fail2;
_copy_from_pil_style((char *)PyArray_DATA((PyArrayObject *)r), nd,
(char *)view->buf, shape, view->strides,
view->suboffsets, view->itemsize);

}
*out = r;
return 0;

fail:
Py_XDECREF(descr);
fail2:
Py_DECREF(memoryview);
return -1;

Expand Down
14 changes: 14 additions & 0 deletions numpy/core/tests/test_multiarray.py
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Original file line number Diff line number Diff line change
Expand Up @@ -5921,6 +5921,20 @@ def test_relaxed_strides(self):
shape, strides = get_buffer_info(arr, ['C_CONTIGUOUS'])
assert_(strides[-1] == 8)

def test_pil_style(self):
try:
import _testbuffer
except ImportError:
raise SkipTest("_testbuffer is not available")

for shape in [(2, 3), (2, 3, 4)]:
data = list(range(np.prod(shape)))
buffer = _testbuffer.ndarray(data, shape, format='i',
flags=_testbuffer.ND_PIL)
a = np.array(buffer)
b = np.array(data, dtype='i').reshape(shape)
yield assert_equal, a, b


class TestArrayAttributeDeletion(object):

Expand Down