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bitmap: add bitmap_weight_from()

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The function calculates a Hamming weight of a bitmap starting from an
arbitrary bit.

Signed-off-by: Yury Norov <ynorov@nvidia.com>
This commit is contained in:
Yury Norov 2025-12-22 14:11:37 -05:00
parent 6c88ba561c
commit bf31ddc14f
2 changed files with 59 additions and 0 deletions
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33
include/linux/bitmap.h
View File

@ -57,6 +57,7 @@ struct device;
* bitmap_weight(src, nbits) Hamming Weight: number set bits
* bitmap_weight_and(src1, src2, nbits) Hamming Weight of and'ed bitmap
* bitmap_weight_andnot(src1, src2, nbits) Hamming Weight of andnot'ed bitmap
* bitmap_weight_from(src, start, end) Hamming Weight starting from @start
* bitmap_set(dst, pos, nbits) Set specified bit area
* bitmap_clear(dst, pos, nbits) Clear specified bit area
* bitmap_find_next_zero_area(buf, len, pos, n, mask) Find bit free area
@ -479,6 +480,38 @@ unsigned long bitmap_weight_andnot(const unsigned long *src1,
return __bitmap_weight_andnot(src1, src2, nbits);
}
/**
* bitmap_weight_from - Hamming weight for a memory region
* @bitmap: The base address
* @start: The bitnumber to starts weighting
* @end: the bitmap size in bits
*
* Returns the number of set bits in the region. If @start >= @end,
* return >= end.
*/
static __always_inline
unsigned long bitmap_weight_from(const unsigned long *bitmap,
unsigned int start, unsigned int end)
{
unsigned long w;
if (unlikely(start >= end))
return end;
if (small_const_nbits(end))
return hweight_long(*bitmap & GENMASK(end - 1, start));
bitmap += start / BITS_PER_LONG;
/* Opencode round_down() to not include math.h */
end -= start & ~(BITS_PER_LONG - 1);
start %= BITS_PER_LONG;
w = bitmap_weight(bitmap, end);
if (start)
w -= hweight_long(*bitmap & BITMAP_LAST_WORD_MASK(start));
return w;
}
static __always_inline
void bitmap_set(unsigned long *map, unsigned int start, unsigned int nbits)
{

26
lib/test_bitmap.c
View File

@ -854,6 +854,31 @@ static void __init test_for_each_set_bit_from(void)
}
}
static void __init test_bitmap_weight(void)
{
unsigned int bit, w1, w2, w;
DECLARE_BITMAP(b, 30);
bitmap_parselist("all:1/2", b, 30);
/* Test inline implementation */
w = bitmap_weight(b, 30);
w1 = bitmap_weight(b, 15);
w2 = bitmap_weight_from(b, 15, 30);
expect_eq_uint(15, w);
expect_eq_uint(8, w1);
expect_eq_uint(7, w2);
/* Test outline implementation */
w = bitmap_weight(exp1, EXP1_IN_BITS);
for (bit = 0; bit < EXP1_IN_BITS; bit++) {
w1 = bitmap_weight(exp1, bit);
w2 = bitmap_weight_from(exp1, bit, EXP1_IN_BITS);
expect_eq_uint(w1 + w2, w);
}
}
static void __init test_for_each_clear_bit(void)
{
DECLARE_BITMAP(orig, 500);
@ -1444,6 +1469,7 @@ static void __init selftest(void)
test_bitmap_const_eval();
test_bitmap_read_write();
test_bitmap_read_perf();
test_bitmap_weight();
test_bitmap_write_perf();
test_find_nth_bit();