util/find.c

/*
 * Taken from Linux kernel version v5.16.
 */
#include "linux/bitmap.h"
#include "linux/find.h"
#include "linux/kernel.h"

unsigned long _find_next_bit(const unsigned long *addr1,
		const unsigned long *addr2, unsigned long nbits,
		unsigned long start, unsigned long invert)
{
	unsigned long tmp, mask;

	if (start >= nbits)
		return nbits;

	tmp = addr1[start / BITS_PER_LONG];
	if (addr2)
		tmp &= addr2[start / BITS_PER_LONG];
	tmp ^= invert;

	/* Handle 1st word. */
	mask = BITMAP_FIRST_WORD_MASK(start);
	tmp &= mask;

	start = round_down(start, BITS_PER_LONG);

	while (!tmp) {
		start += BITS_PER_LONG;
		if (start >= nbits)
			return nbits;

		tmp = addr1[start / BITS_PER_LONG];
		if (addr2)
			tmp &= addr2[start / BITS_PER_LONG];
		tmp ^= invert;
	}

	return min(start + __builtin_ctzl(tmp), nbits);
}