On Thu, Feb 22, 2024 at 03:22:16PM +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. Mine SoB is enough for a credit, but thank you :-) ... > +/** > + * bitmap_gather - Gather a bitmap according to given mask > + * @dst: gathered bitmap > + * @src: scattered bitmap > + * @mask: mask representing bits to extract from in the scattered bitmap > + * @nbits: number of bits in each of these bitmaps > + * > + * Gathers bitmap with sparse bits according to the given @mask. > + * > + * Example: > + * If @src bitmap = 0x0302, with @mask = 0x1313, @dst will be 0x001a. > + * > + * Or in binary form > + * @src @mask @dst > + * 0000001100000010 0001001100010011 0000000000011010 > + * > + * (Bits 0, 1, 4, 8, 9, 12 are copied to the bits 0, 1, 2, 3, 4, 5) > + * > + * A more 'visual' description of the operation: > + * mask: ...v..vv...v..vv > + * src: 0000001100000010 > + * ^ ^^ ^ 0 > + * | || | 10 > + * | || > 010 > + * | |+--> 1010 > + * | +--> 11010 > + * +----> 011010 > + * dst: 0000000000011010 Cool! > + * A relationship exists between bitmap_gather() and bitmap_scatter() (See Either '... (see' or '(). 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. This paragraph... > + * 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. ...seems duplicating this one. I would drop the latter one. > + */ -- With Best Regards, Andy Shevchenko