[Numpy-discussion] GSOC 2013

Kurt Smith kwmsmith@gmail....
Tue Mar 5 12:14:22 CST 2013


On Tue, Mar 5, 2013 at 1:45 AM, Eric Firing <efiring@hawaii.edu> wrote:
> On 2013/03/04 9:01 PM, Nicolas Rougier wrote:
>>> >This made me think of a serious performance limitation of structured dtypes: a
>>> >structured dtype is always "packed", which may lead to terrible byte alignment
>>> >for common types.  For instance, `dtype([('a', 'u1'), ('b',
>>> >'u8')]).itemsize == 9`,
>>> >meaning that the 8-byte integer is not aligned as an equivalent C-struct's
>>> >would be, leading to all sorts of horrors at the cache and register level.
>
> Doesn't the "align" kwarg of np.dtype do what you want?
>
> In [2]: dt = np.dtype(dict(names=['a', 'b'], formats=['u1', 'u8']),
> align=True)
>
> In [3]: dt.itemsize
> Out[3]: 16

Thanks!  That's what I get for not checking before posting.

Consider this my vote to make `aligned=True` the default.

>
> Eric
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