On Tue, 2022-01-18 at 18:29 +0100, Benoit Gschwind wrote: > Hello Sebastian, > > Thanks for detail. > > The last call has the NPY_ARRAY_C_CONTIGUOUS and NPY_ARRAY_ALIGNED, > thus I guess it can be no-op most of the time but for some unknown > case > it's may be safer ?
Ah, yes, you are right, and it should indeed by very quick, anyway. My
guess is, that you can do _only_ the last call with the appropriate
`datetime64[ms]` descriptor passed in.
(Since whatever C-code that follows is allowed to work with datetime64
as if it were int64.)
Cheers,
Sebastian
>
> Best regards
>
> On Tue, 2022-01-18 at 09:22 -0600, Sebastian Berg wrote:
> > On Tue, 2022-01-18 at 14:56 +0100, Benoit Gschwind wrote:
> > > Hello,
> > >
> > > I using the following code:
> > >
> > > if (PyArray_TYPE(arr1) == NPY_DATETIME) {
> > > // Ensure datetime64[ms]
> > > auto tmp =
> > > reinterpret_cast<PyArrayObject*>(PyObject_CallMethod(reinterpret_
> > > ca
> > > st
> > > <PyObject*>(arr1), "astype", "(s)", "datetime64[ms]"));
> > > std::swap(arr1, tmp);
> > > Py_XDECREF(tmp);
> > > // Ensure integer
> > > tmp =
> > > reinterpret_cast<PyArrayObject*>(PyObject_CallMethod(reinterpret_
> > > ca
> > > st
> > > <PyObject*>(arr1), "astype", "(s)", "i8"));
> > > std::swap(arr1, tmp);
> > > Py_XDECREF(tmp);
> > > tmp =
> > > reinterpret_cast<PyArrayObject*>(PyArray_FromArray(arr1,
> > > PyArray_DescrFromType(NPY_INT64), NPY_ARRAY_IN_ARRAY));
> > > std::swap(arr1, tmp);
> > > Py_XDECREF(tmp);
> > > }
> > >
> > > First, if something is wrong with my code let me known. Then I
> > > wonder
> > > if I can have a safe shortcut to avoid converting datetime64 to
> > > i8.
> > > I
> > > guess the internal data of datetime64[ms] is i8 thus copying and
> > > casting the array may be avoided.
> >
> > Yes, you can assume datetime64 is stored as an i8 with the unit and
> > possible byteswapping. Both of which, your initial cast will
> > ensure.
> >
> > The internal data is i8, except for the special NaT value.
> >
> > Code-wise, you can avoid calling `astype`, but if you do (also in
> > python), I suggest to pass `copy=False`, so that it does not copy
> > if
> > it
> > clearly is not necessary (I am hoping to improve on the "clearly"
> > here
> > at some point).
> >
> > The last call again seems to be a no-op? Just the last call with
> > the
> > correct `datetime64[ms]` descriptor could be enough.
> >
> > Cheers,
> >
> > Sebastian
> >
> >
> > >
> > > Thanks by advance
> > > Best regards.
> > >
> > >
> > > _______________________________________________
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> > > Member address: sebast...@sipsolutions.net
> > >
> >
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>
>
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