[Numpy-discussion] Proposal for adding bit_count

[Ganesh Kathiresan]

>
> Should `np.ndarray.bit_count()` exist?  I tend against this;


Thanks for the info Sebastian, I agree with this as we can stick to what
Python offers.

Should `np.bit_count` exist?  Having it on the int* types may be sufficient.


Hey Stephan, regarding this, I felt we could support it in the same lines NumPy
Mathematical Functions
<https://numpy.org/doc/stable/reference/routines.math.html>, something like
GCD perhaps, where we do not have `np.ndarray.gcd` but do have an `np.gcd`

What is the max value of the count?  64?  If so it can go in a uint8.


This makes sense yeah, will make this change, thanks for the suggestion.

Also, an interesting future proposal can be to club all the bitwise
functions into a single "namespace" of sorts and have np.bits.*. This has
already been suggested in this comment
<https://github.com/numpy/numpy/issues/16325#issuecomment-869182363> and I
feel this would be a clean addition and we can support other useful
functions as well.

Regards,
Ganesh

On Tue, Aug 3, 2021 at 9:18 PM Sebastian Berg <sebastian at sipsolutions.net>
wrote:

> On Mon, 2021-08-02 at 13:10 -0700, Stefan van der Walt wrote:
> > On Mon, Aug 2, 2021, at 10:50, Sebastian Berg wrote:
> > > * Should `np.ndarray.bit_count()` exist?  I tend against this;
> > >   but we should have it on (integer) scalars to mirror the
> > >   Python `int`.
> >
> > Should `np.bit_count` exist?  Having it on the int* types may be
> > sufficient.
>
> Right, we could add it only to the integer scalars mostly for Python
> compatibility.  The PR suggests to create a ufunc to make the feature
> available to typical NumPy code (allow using it with arrays).
>
> >
> > > * The return value is currently the same type as the input.  That
> > >   means that: `np.bit_count(uint8)` returns the count as `uint8`
> > >   while `np.bit_count(int32)` returns it as `int32`, etc.
> >
> > What is the max value of the count?  64?  If so it can go in a uint8.
>
> Yes, uint8 would even work for 128 bit integers.  I was a bit unsure
> about this, since we rarely create non-default integer arrays unless
> prompted, but it is a good option as well.
>
> Cheers,
>
> Sebastian
>
>
> >
> > Stéfan
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