On Tue, Oct 06, 2020 at 02:52:16PM +0530, Syed Nayyar Waris wrote:
> This macro iterates for each group of bits (clump) with set bits,
> within a bitmap memory region. For each iteration, "start" is set to
> the bit offset of the found clump, while the respective clump value is
> stored to the location pointed by "clump". Additionally, the
> bitmap_get_value() and bitmap_set_value() functions are introduced to
> respectively get and set a value of n-bits in a bitmap memory region.
> The n-bits can have any size less than or equal to BITS_PER_LONG.
> Moreover, during setting value of n-bit in bitmap, if a situation arise
> that the width of next n-bit is exceeding the word boundary, then it
> will divide itself such that some portion of it is stored in that word,
> while the remaining portion is stored in the next higher word. Similar
> situation occurs while retrieving the value from bitmap.
...
> @@ -75,7 +75,11 @@
> * bitmap_from_arr32(dst, buf, nbits) Copy nbits from u32[] buf to dst
> * bitmap_to_arr32(buf, src, nbits) Copy nbits from buf to u32[] dst
> * bitmap_get_value8(map, start) Get 8bit value from map at start
> + * bitmap_get_value(map, start, nbits) Get bit value of size
> + * 'nbits' from map at start
> * bitmap_set_value8(map, value, start) Set 8bit value to map at start
> + * bitmap_set_value(map, value, start, nbits) Set bit value of size 'nbits'
> + * of map at start
Formatting here is done with solely spaces, no TABs.
...
> +/**
> + * bitmap_get_value - get a value of n-bits from the memory region
> + * @map: address to the bitmap memory region
> + * @start: bit offset of the n-bit value
> + * @nbits: size of value in bits (must be between 1 and BITS_PER_LONG inclusive).
> + * nbits less than 1 or more than BITS_PER_LONG causes undefined behaviour.
Please, detach this from field description and move to a main description.
> + *
> + * Returns value of nbits located at the @start bit offset within the @map
> + * memory region.
> + */
...
> + return (map[index] >> offset) & GENMASK(nbits - 1, 0);
Have you considered to use rather BIT{_ULL}(nbits) - 1?
It maybe better for code generation.
...
> +/**
> + * bitmap_set_value - set n-bit value within a memory region
> + * @map: address to the bitmap memory region
> + * @value: value of nbits
> + * @start: bit offset of the n-bit value
> + * @nbits: size of value in bits (must be between 1 and BITS_PER_LONG inclusive).
> + * nbits less than 1 or more than BITS_PER_LONG causes undefined behaviour.
Please, detach this from field description and move to a main description.
> + */
...
> + value &= GENMASK(nbits - 1, 0);
Ditto.
> + map[index] &= ~(GENMASK(nbits + offset - 1, offset));
Last time I checked such GENMASK) use, it gave a lot of code when
GENMASK(nbits - 1, 0) << offset works much better, but see also above.
--
With Best Regards,
Andy Shevchenko
