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ENH: Allow views using smaller coprime itemsizes #6097

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ENH: Allow views using smaller coprime itemsizes #6097

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23 changes: 6 additions & 17 deletions numpy/core/src/multiarray/getset.c
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Original file line number Diff line number Diff line change
Expand Up @@ -431,7 +431,7 @@ static int
array_descr_set(PyArrayObject *self, PyObject *arg)
{
PyArray_Descr *newtype = NULL;
npy_intp newdim;
npy_intp nbytes;
int i;
char *msg = "new type not compatible with array.";
PyObject *safe;
Expand Down Expand Up @@ -493,28 +493,17 @@ array_descr_set(PyArrayObject *self, PyObject *arg)
else {
i = 0;
}
if (newtype->elsize < PyArray_DESCR(self)->elsize) {
/*
* if it is compatible increase the size of the
* dimension at end (or at the front for NPY_ARRAY_F_CONTIGUOUS)
*/
if (PyArray_DESCR(self)->elsize % newtype->elsize != 0) {
goto fail;
}
newdim = PyArray_DESCR(self)->elsize / newtype->elsize;
PyArray_DIMS(self)[i] *= newdim;
PyArray_STRIDES(self)[i] = newtype->elsize;
}
else if (newtype->elsize > PyArray_DESCR(self)->elsize) {

if (newtype->elsize != PyArray_DESCR(self)->elsize) {
/*
* Determine if last (or first if NPY_ARRAY_F_CONTIGUOUS) dimension
* is compatible
*/
newdim = PyArray_DIMS(self)[i] * PyArray_DESCR(self)->elsize;
if ((newdim % newtype->elsize) != 0) {
nbytes = PyArray_DIMS(self)[i] * PyArray_DESCR(self)->elsize;
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@charris charris Jul 20, 2015

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Can use PyArray_DIM(self, i) here.

if ((nbytes % newtype->elsize) != 0) {
goto fail;
}
PyArray_DIMS(self)[i] = newdim / newtype->elsize;
PyArray_DIMS(self)[i] = nbytes / newtype->elsize;
PyArray_STRIDES(self)[i] = newtype->elsize;
}

Expand Down
10 changes: 10 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 @@ -5707,6 +5707,16 @@ def scanView(d1, otype):
'itemsize': 4*psize})
assert_equal(scanView(overlapped, 'p'), [0, 1, 3*psize-1, 3*psize])

def test_coprime_itemsizes(self):
# test we can view using coprime itemsizes, as long as the array length
# is suitable

np.zeros(2, 'p,p,p').view('p,p')
assert_raises(ValueError, np.zeros(3, 'p,p,p').view, 'p,p')

np.zeros(3, 'p,p').view('p,p,p')
assert_raises(ValueError, np.zeros(2, 'p,p').view, 'p,p,p')


class TestArrayPriority(TestCase):
# This will go away when __array_priority__ is settled, meanwhile
Expand Down