linux/lib/find_bit.c

// SPDX-License-Identifier: GPL-2.0-or-later
/* bit search implementation
 *
 * Copyright (C) 2004 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * Copyright (C) 2008 IBM Corporation
 * 'find_last_bit' is written by Rusty Russell <rusty@rustcorp.com.au>
 * (Inspired by David Howell's find_next_bit implementation)
 *
 * Rewritten by Yury Norov <yury.norov@gmail.com> to decrease
 * size and improve performance, 2015.
 */

#include <linux/bitops.h>
#include <linux/bitmap.h>
#include <linux/export.h>
#include <linux/math.h>
#include <linux/minmax.h>
#include <linux/swab.h>

/*
 * Common helper for find_bit() function family
 * @FETCH: The expression that fetches and pre-processes each word of bitmap(s)
 * @MUNGE: The expression that post-processes a word containing found bit (may be empty)
 * @size: The bitmap size in bits
 */
#define FIND_FIRST_BIT(FETCH, MUNGE, size)					\
({										\
	unsigned long idx, val, sz = (size);					\
										\
	for (idx = 0; idx * BITS_PER_LONG < sz; idx++) {			\
		val = (FETCH);							\
		if (val) {							\
			sz = min(idx * BITS_PER_LONG + __ffs(MUNGE(val)), sz);	\
			break;							\
		}								\
	}									\
										\
	sz;									\
})

#if !defined(find_next_bit) || !defined(find_next_zero_bit) ||			\
	!defined(find_next_bit_le) || !defined(find_next_zero_bit_le) ||	\
	!defined(find_next_and_bit)
/*
 * This is a common helper function for find_next_bit, find_next_zero_bit, and
 * find_next_and_bit. The differences are:
 *  - The "invert" argument, which is XORed with each fetched word before
 *    searching it for one bits.
 *  - The optional "addr2", which is anded with "addr1" if present.
 */
unsigned long _find_next_bit(const unsigned long *addr1,
		const unsigned long *addr2, unsigned long nbits,
		unsigned long start, unsigned long invert, unsigned long le)
{
	unsigned long tmp, mask;

	if (unlikely(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);
	if (le)
		mask = swab(mask);

	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;
	}

	if (le)
		tmp = swab(tmp);

	return min(start + __ffs(tmp), nbits);
}
EXPORT_SYMBOL(_find_next_bit);
#endif

#ifndef find_first_bit
/*
 * Find the first set bit in a memory region.
 */
unsigned long _find_first_bit(const unsigned long *addr, unsigned long size)
{
	return FIND_FIRST_BIT(addr[idx], /* nop */, size);
}
EXPORT_SYMBOL(_find_first_bit);
#endif

#ifndef find_first_and_bit
/*
 * Find the first set bit in two memory regions.
 */
unsigned long _find_first_and_bit(const unsigned long *addr1,
				  const unsigned long *addr2,
				  unsigned long size)
{
	return FIND_FIRST_BIT(addr1[idx] & addr2[idx], /* nop */, size);
}
EXPORT_SYMBOL(_find_first_and_bit);
#endif

#ifndef find_first_zero_bit
/*
 * Find the first cleared bit in a memory region.
 */
unsigned long _find_first_zero_bit(const unsigned long *addr, unsigned long size)
{
	return FIND_FIRST_BIT(~addr[idx], /* nop */, size);
}
EXPORT_SYMBOL(_find_first_zero_bit);
#endif

#ifndef find_last_bit
unsigned long _find_last_bit(const unsigned long *addr, unsigned long size)
{
	if (size) {
		unsigned long val = BITMAP_LAST_WORD_MASK(size);
		unsigned long idx = (size-1) / BITS_PER_LONG;

		do {
			val &= addr[idx];
			if (val)
				return idx * BITS_PER_LONG + __fls(val);

			val = ~0ul;
		} while (idx--);
	}
	return size;
}
EXPORT_SYMBOL(_find_last_bit);
#endif

unsigned long find_next_clump8(unsigned long *clump, const unsigned long *addr,
			       unsigned long size, unsigned long offset)
{
	offset = find_next_bit(addr, size, offset);
	if (offset == size)
		return size;

	offset = round_down(offset, 8);
	*clump = bitmap_get_value8(addr, offset);

	return offset;
}
EXPORT_SYMBOL(find_next_clump8);