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don't copy data when changing shape #145

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don't copy data when changing shape #145

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96c3bb2
Use PyArray_Newshape instead of PyArray_Reshape
tecki Aug 24, 2011
40df395
Do not copy array if shape is set
tecki Aug 24, 2011
82b3c0d
avoid doubling code
tecki Aug 24, 2011
7e33e79
white space corrected
tecki Oct 2, 2011
f7f409b
add comments for shape.c:_Newshape
tecki Oct 2, 2011
f220ecf
simpler version for nocopy-reshape
tecki Oct 2, 2011
42f9e04
don't expose NPY_NOCOPY in API
tecki Mar 13, 2012
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5 changes: 4 additions & 1 deletion numpy/core/include/numpy/ndarraytypes.h
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Original file line number Diff line number Diff line change
Expand Up @@ -187,7 +187,10 @@ typedef enum {
/* Fortran order */
NPY_FORTRANORDER=1,
/* An order as close to the inputs as possible */
NPY_KEEPORDER=2
NPY_KEEPORDER=2,
/* Don't copy data, so order obviously is kept.
* used as special value in PyArray_Newshape */
NPY_NOCOPY=3
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I think this may be a bad idea. This is a general enum in the publicly exposed API, so a special value for one API function isn't appropriate. Further, NOCOPY seems to have roughly the same meaning as KEEPORDER.

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No, NOCOPY has a very different meaning from KEEPORDER. The latter means that the order ought to
be kept (hence the name) while copying, while NOCOPY means that the data should not be copied.

} NPY_ORDER;

/* For specifying allowed casting in operations which support it */
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13 changes: 6 additions & 7 deletions numpy/core/src/multiarray/getset.c
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Expand Up @@ -44,17 +44,16 @@ array_shape_set(PyArrayObject *self, PyObject *val)
{
int nd;
PyArrayObject *ret;
PyArray_Dims newdims;

/* Assumes C-order */
ret = (PyArrayObject *)PyArray_Reshape(self, val);
if (ret == NULL) {
if (!PyArray_IntpConverter(val, &newdims)) {
return -1;
}
if (PyArray_DATA(ret) != PyArray_DATA(self)) {
Py_DECREF(ret);
PyErr_SetString(PyExc_AttributeError,
"incompatible shape for a non-contiguous "\
"array");
ret = (PyArrayObject *)PyArray_Newshape(self, &newdims, NPY_NOCOPY);
PyDimMem_FREE(newdims.ptr);

if (ret == NULL) {
return -1;
}

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20 changes: 15 additions & 5 deletions numpy/core/src/multiarray/shape.c
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Expand Up @@ -167,7 +167,11 @@ PyArray_Resize(PyArrayObject *self, PyArray_Dims *newshape, int refcheck,
* Returns a new array
* with the new shape from the data
* in the old array --- order-perspective depends on order argument.
* copy-only-if-necessary
* The data is copied only if it is necessary. Otherwise a view
* on the original array is returned. Copying can be prevented by setting
* `order` to the special value `NPY_NOCOPY`, which is equivalent to
* `NPY_CORDER`, just that an `AttributeError` is flagged if reshaping
* is impossible without copying.
*/

/*NUMPY_API
Expand Down Expand Up @@ -236,16 +240,17 @@ PyArray_Newshape(PyArrayObject *self, PyArray_Dims *newdims,
(((PyArray_CHKFLAGS(self, NPY_ARRAY_C_CONTIGUOUS) &&
order == NPY_FORTRANORDER) ||
(PyArray_CHKFLAGS(self, NPY_ARRAY_F_CONTIGUOUS) &&
order == NPY_CORDER)) && (PyArray_NDIM(self) > 1))) {
(order == NPY_CORDER || order == NPY_NOCOPY)
)) && (PyArray_NDIM(self) > 1))) {
int success = 0;
success = _attempt_nocopy_reshape(self,n,dimensions,
newstrides,order);
success = _attempt_nocopy_reshape(self,n,dimensions, newstrides,
order == NPY_NOCOPY ? NPY_CORDER : order);
if (success) {
/* no need to copy the array after all */
strides = newstrides;
flags = PyArray_FLAGS(self);
}
else {
else if (order != NPY_NOCOPY) {
PyObject *new;
new = PyArray_NewCopy(self, order);
if (new == NULL) {
Expand All @@ -255,6 +260,11 @@ PyArray_Newshape(PyArrayObject *self, PyArray_Dims *newdims,
self = (PyArrayObject *)new;
flags = PyArray_FLAGS(self);
}
else {
PyErr_SetString(PyExc_AttributeError,
"incompatible shape for a non-contiguous array");
return NULL;
}
}

/* We always have to interpret the contiguous buffer correctly */
Expand Down