Re: [PATCH 3/6] bitops: bitmap helper to set variable length values

Andy Shevchenko
2022-07-13T20:15:04Z

On Wed, Jul 13, 2022 at 9:44 PM Yury Norov <yury.norov@gmail.com> wrote:
> On Wed, Jul 13, 2022 at 09:10:33PM +0200, Andy Shevchenko wrote:
> > On Wed, Jul 13, 2022 at 8:56 PM Yury Norov <yury.norov@gmail.com> wrote:
> > > On Wed, Jul 13, 2022 at 06:31:59PM +0200, Sebastian Fricke wrote:
> >
> > ...
> >
> > > I'd suggest you to try implementing
> > > bitmap_copy_from(dst, src, dst_off, len)
> > > or even
> > > bitmap_copy_from(dst, dst_off, src, src_off, len)
> > > if you expect that you'll need more flexibility in the future.
> >
> > Do you think it would be useful?
> >
> > We have bitmap_replace() & bitmap_remap(). Wouldn't that be enough?
>
> bitmap_replace and bitmap_remap have no an 'offset' parameter.

True.

But then it's a bit too generic to have this src_off, no?

I would rather expect for asymmetrical bitmaps that the other side
will be either one of the fixed width types (it makes sense to have
for 32- or 64-bit arguments.

When you have a source bitmap of x bits and you would like to copy it
into a y-bit one, I would think that either you have a small amount of
bits in x anyway, or x is a full-sized bitmap (same order as y). Also
keep in mind that granularity is long, so less than long it makes no
sense.

bitmap_copy_from_T(unsigned long *map, start, len, T src),

where T is type, start is the offset in map, len is the amount of bits
from src starting from 0. That's what is required in most of the cases
I believe.

--
With Best Regards,
Andy Shevchenko