On Mon, Jun 15, 2020 at 06:21:18PM +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 value of n-bits from bitmap.
On the second view...
> +static inline unsigned long bitmap_get_value(const unsigned long *map,
> + unsigned long start,
> + unsigned long nbits)
> +{
> + const size_t index = BIT_WORD(start);
> + const unsigned long offset = start % BITS_PER_LONG;
> + const unsigned long ceiling = roundup(start + 1, BITS_PER_LONG);
This perhaps should use round_up()
> + const unsigned long space = ceiling - start;
And I think I see a scenario to complain.
If start == 0, then ceiling will be 64.
space == 64. Not good.
> + unsigned long value_low, value_high;
> +
> + if (space >= nbits)
> + return (map[index] >> offset) & GENMASK(nbits - 1, 0);
> + else {
> + value_low = map[index] & BITMAP_FIRST_WORD_MASK(start);
> + value_high = map[index + 1] & BITMAP_LAST_WORD_MASK(start + nbits);
> + return (value_low >> offset) | (value_high << space);
> + }
> +}
...
> +/**
> + * 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
> + */
> +static inline void bitmap_set_value(unsigned long *map,
> + unsigned long value,
> + unsigned long start, unsigned long nbits)
> +{
> + const size_t index = BIT_WORD(start);
> + const unsigned long offset = start % BITS_PER_LONG;
> + const unsigned long ceiling = roundup(start + 1, BITS_PER_LONG);
> + const unsigned long space = ceiling - start;
Ditto for both lines.
> + value &= GENMASK(nbits - 1, 0);
> +
> + if (space >= nbits) {
> + map[index] &= ~(GENMASK(nbits + offset - 1, offset));
> + map[index] |= value << offset;
> + } else {
> + map[index] &= ~BITMAP_FIRST_WORD_MASK(start);
> + map[index] |= value << offset;
> + map[index + 1] &= ~BITMAP_LAST_WORD_MASK(start + nbits);
> + map[index + 1] |= (value >> space);
> + }
> +}
--
With Best Regards,
Andy Shevchenko
