Re: [PATCH v6 3/5] lib/bitmap: Introduce bitmap_scatter() and bitmap_gather() helpers

[Yury Norov]

On Wed, Mar 06, 2024 at 09:07:19AM +0100, Herve Codina wrote:
> From: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> 
> 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.
> 
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> Link: https://lore.kernel.org/lkml/20230926052007.3917389-3-andriy.shevchenko@xxxxxxxxxxxxxxx/
> Co-developed-by: Herve Codina <herve.codina@xxxxxxxxxxx>
> Signed-off-by: Herve Codina <herve.codina@xxxxxxxxxxx>

Signed-off-by: Yury Norov <yury.norov@xxxxxxxxx>

Would you like to move this with the rest of the series? If so please
pull my Sof-by, otherwise I can move it with bitmap-for-next.

> ---
>  include/linux/bitmap.h | 101 +++++++++++++++++++++++++++++++++++++++++
>  lib/test_bitmap.c      |  42 +++++++++++++++++
>  2 files changed, 143 insertions(+)
> 
> diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
> index 99451431e4d6..049ba20911c5 100644
> --- a/include/linux/bitmap.h
> +++ b/include/linux/bitmap.h
> @@ -62,6 +62,8 @@ struct device;
>   *  bitmap_shift_left(dst, src, n, nbits)       *dst = *src << n
>   *  bitmap_cut(dst, src, first, n, nbits)       Cut n bits from first, copy rest
>   *  bitmap_replace(dst, old, new, mask, nbits)  *dst = (*old & ~(*mask)) | (*new & *mask)
> + *  bitmap_scatter(dst, src, mask, nbits)	*dst = map(dense, sparse)(src)
> + *  bitmap_gather(dst, src, mask, nbits)	*dst = map(sparse, dense)(src)
>   *  bitmap_remap(dst, src, old, new, nbits)     *dst = map(old, new)(src)
>   *  bitmap_bitremap(oldbit, old, new, nbits)    newbit = map(old, new)(oldbit)
>   *  bitmap_onto(dst, orig, relmap, nbits)       *dst = orig relative to relmap
> @@ -487,6 +489,105 @@ static inline void bitmap_replace(unsigned long *dst,
>  		__bitmap_replace(dst, old, new, mask, nbits);
>  }
>  
> +/**
> + * bitmap_scatter - Scatter a bitmap according to the given mask
> + * @dst: scattered bitmap
> + * @src: gathered bitmap
> + * @mask: mask representing bits to assign to in the scattered bitmap
> + * @nbits: number of bits in each of these bitmaps
> + *
> + * Scatters bitmap with sequential bits according to the given @mask.
> + *
> + * Example:
> + * If @src bitmap = 0x005a, with @mask = 0x1313, @dst will be 0x0302.
> + *
> + * Or in binary form
> + * @src			@mask			@dst
> + * 0000000001011010	0001001100010011	0000001100000010
> + *
> + * (Bits 0, 1, 2, 3, 4, 5 are copied to the bits 0, 1, 4, 8, 9, 12)
> + *
> + * A more 'visual' description of the operation:
> + * src:  0000000001011010
> + *                 ||||||
> + *          +------+|||||
> + *          |  +----+||||
> + *          |  |+----+|||
> + *          |  ||   +-+||
> + *          |  ||   |  ||
> + * mask: ...v..vv...v..vv
> + *       ...0..11...0..10
> + * dst:  0000001100000010
> + *
> + * A relationship exists between bitmap_scatter() and bitmap_gather().
> + * bitmap_gather() can be seen as the 'reverse' bitmap_scatter() operation.
> + * See bitmap_scatter() for details related to this relationship.
> + */
> +static inline void bitmap_scatter(unsigned long *dst, const unsigned long *src,
> +				  const unsigned long *mask, unsigned int nbits)
> +{
> +	unsigned int n = 0;
> +	unsigned int bit;
> +
> +	bitmap_zero(dst, nbits);
> +
> +	for_each_set_bit(bit, mask, nbits)
> +		__assign_bit(bit, dst, test_bit(n++, src));
> +}
> +
> +/**
> + * 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
> + *
> + * 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.
> + */
> +static inline void bitmap_gather(unsigned long *dst, const unsigned long *src,
> +				 const unsigned long *mask, unsigned int nbits)
> +{
> +	unsigned int n = 0;
> +	unsigned int bit;
> +
> +	bitmap_zero(dst, nbits);
> +
> +	for_each_set_bit(bit, mask, nbits)
> +		__assign_bit(n++, dst, test_bit(bit, src));
> +}
> +
>  static inline void bitmap_next_set_region(unsigned long *bitmap,
>  					  unsigned int *rs, unsigned int *re,
>  					  unsigned int end)
> diff --git a/lib/test_bitmap.c b/lib/test_bitmap.c
> index 65f22c2578b0..6b2b33579f56 100644
> --- a/lib/test_bitmap.c
> +++ b/lib/test_bitmap.c
> @@ -380,6 +380,47 @@ static void __init test_replace(void)
>  	expect_eq_bitmap(bmap, exp3_1_0, nbits);
>  }
>  
> +static const unsigned long sg_mask[] __initconst = {
> +	BITMAP_FROM_U64(0x000000000000035aULL),
> +};
> +
> +static const unsigned long sg_src[] __initconst = {
> +	BITMAP_FROM_U64(0x0000000000000667ULL),
> +};
> +
> +static const unsigned long sg_gather_exp[] __initconst = {
> +	BITMAP_FROM_U64(0x0000000000000029ULL),
> +};
> +
> +static const unsigned long sg_scatter_exp[] __initconst = {
> +	BITMAP_FROM_U64(0x000000000000021aULL),
> +};
> +
> +static void __init test_bitmap_sg(void)
> +{
> +	unsigned int nbits = 64;
> +	DECLARE_BITMAP(bmap_gather, 100);
> +	DECLARE_BITMAP(bmap_scatter, 100);
> +	DECLARE_BITMAP(bmap_tmp, 100);
> +	DECLARE_BITMAP(bmap_res, 100);
> +
> +	/* Simple gather call */
> +	bitmap_zero(bmap_gather, 100);
> +	bitmap_gather(bmap_gather, sg_src, sg_mask, nbits);
> +	expect_eq_bitmap(sg_gather_exp, bmap_gather, nbits);
> +
> +	/* Simple scatter call */
> +	bitmap_zero(bmap_scatter, 100);
> +	bitmap_scatter(bmap_scatter, sg_src, sg_mask, nbits);
> +	expect_eq_bitmap(sg_scatter_exp, bmap_scatter, nbits);
> +
> +	/* Scatter/gather relationship */
> +	bitmap_zero(bmap_tmp, 100);
> +	bitmap_gather(bmap_tmp, bmap_scatter, sg_mask, nbits);
> +	bitmap_scatter(bmap_res, bmap_tmp, sg_mask, nbits);
> +	expect_eq_bitmap(bmap_scatter, bmap_res, nbits);
> +}
> +
>  #define PARSE_TIME	0x1
>  #define NO_LEN		0x2
>  
> @@ -1252,6 +1293,7 @@ static void __init selftest(void)
>  	test_copy();
>  	test_bitmap_region();
>  	test_replace();
> +	test_bitmap_sg();
>  	test_bitmap_arr32();
>  	test_bitmap_arr64();
>  	test_bitmap_parse();
> -- 
> 2.43.0