On Thu, Feb 29, 2024 at 03:15:51PM +0100, Herve Codina wrote: > From: Andy Shevchenko <andriy.shevche...@linux.intel.com> > > These helpers scatters or gathers a bitmap with the help of the mask > position bits parameter. > > bitmap_scatter() does the following: > src: 0000000001011010 > |||||| > +------+||||| > | +----+|||| > | |+----+||| > | || +-+|| > | || | || > mask: ...v..vv...v..vv > ...0..11...0..10 > dst: 0000001100000010 > > and bitmap_gather() performs this one: > mask: ...v..vv...v..vv > src: 0000001100000010 > ^ ^^ ^ 0 > | || | 10 > | || > 010 > | |+--> 1010 > | +--> 11010 > +----> 011010 > dst: 0000000000011010 > > bitmap_gather() can the seen as the reverse bitmap_scatter() operation.
> The original work was done by Andy Shevchenko. As I said, it's too much credit :-) ... > + * A relationship exists between bitmap_gather() and bitmap_scatter(). See > + * bitmap_scatter() for the bitmap scatter detailed operations. > + * Suppose scattered computed using bitmap_scatter(scattered, src, mask, n). > + * The operation bitmap_gather(result, scattered, mask, n) leads to a result > + * equal or equivalent to src. > + * > + * The result can be 'equivalent' because bitmap_scatter() and > bitmap_gather() > + * are not bijective. > + * The result and src values are equivalent in that sense that a call to > + * bitmap_scatter(res, src, mask, n) and a call to bitmap_scatter(res, > result, > + * mask, n) will lead to the same res value. For better readability I wouldn't break API calls, hence The result and src values are equivalent in that sense that a call to bitmap_scatter(res, src, mask, n) and a call to bitmap_scatter(res, result, mask, n) will lead to the same res value. -- With Best Regards, Andy Shevchenko