[Numpy-discussion] Proposal for adding bit_count

[Sebastian Berg]

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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