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Commit c7f612cd authored by Akinobu Mita's avatar Akinobu Mita Committed by Linus Torvalds
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[PATCH] bitops: generic find_{next,first}{,_zero}_bit() 



This patch introduces the C-language equivalents of the functions below:

unsigned logn find_next_bit(const unsigned long *addr, unsigned long size,
                            unsigned long offset);
unsigned long find_next_zero_bit(const unsigned long *addr, unsigned long size,
                                 unsigned long offset);
unsigned long find_first_zero_bit(const unsigned long *addr,
                                  unsigned long size);
unsigned long find_first_bit(const unsigned long *addr, unsigned long size);

In include/asm-generic/bitops/find.h

This code largely copied from: arch/powerpc/lib/bitops.c

Signed-off-by: default avatarAkinobu Mita <mita@miraclelinux.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 2dfc383a

include/asm-generic/bitops/find.h

0 → 100644
+13 −0
Original line number Diff line number Diff line 
#ifndef _ASM_GENERIC_BITOPS_FIND_H_

#define _ASM_GENERIC_BITOPS_FIND_H_



extern unsigned long find_next_bit(const unsigned long *addr, unsigned long

		size, unsigned long offset);



extern unsigned long find_next_zero_bit(const unsigned long *addr, unsigned

		long size, unsigned long offset);



#define find_first_bit(addr, size) find_next_bit((addr), (size), 0)

#define find_first_zero_bit(addr, size) find_next_zero_bit((addr), (size), 0)



#endif /*_ASM_GENERIC_BITOPS_FIND_H_ */

lib/find_next_bit.c

+81 −31
Original line number Diff line number Diff line
@@ -11,48 +11,98 @@ 


#include <linux/bitops.h>

#include <linux/module.h>

#include <asm/types.h>



int find_next_bit(const unsigned long *addr, int size, int offset)

#define BITOP_WORD(nr)		((nr) / BITS_PER_LONG)



/**

 * find_next_bit - find the next set bit in a memory region

 * @addr: The address to base the search on

 * @offset: The bitnumber to start searching at

 * @size: The maximum size to search

 */

unsigned long find_next_bit(const unsigned long *addr, unsigned long size,

		unsigned long offset)

{

	const unsigned long *base;

	const int NBITS = sizeof(*addr) * 8;

	const unsigned long *p = addr + BITOP_WORD(offset);

	unsigned long result = offset & ~(BITS_PER_LONG-1);

	unsigned long tmp;



	base = addr;

	if (offset >= size)

		return size;

	size -= result;

	offset %= BITS_PER_LONG;

	if (offset) {

		int suboffset;



		addr += offset / NBITS;



		suboffset = offset % NBITS;

		if (suboffset) {

			tmp = *addr;

			tmp >>= suboffset;

		tmp = *(p++);

		tmp &= (~0UL << offset);

		if (size < BITS_PER_LONG)

			goto found_first;

		if (tmp)

				goto finish;

			goto found_middle;

		size -= BITS_PER_LONG;

		result += BITS_PER_LONG;

	}

	while (size & ~(BITS_PER_LONG-1)) {

		if ((tmp = *(p++)))

			goto found_middle;

		result += BITS_PER_LONG;

		size -= BITS_PER_LONG;

	}

	if (!size)

		return result;

	tmp = *p;



		addr++;

found_first:

	tmp &= (~0UL >> (BITS_PER_LONG - size));

	if (tmp == 0UL)		/* Are any bits set? */

		return result + size;	/* Nope. */

found_middle:

	return result + __ffs(tmp);

}



	while ((tmp = *addr) == 0)

		addr++;

EXPORT_SYMBOL(find_next_bit);



	offset = (addr - base) * NBITS;

/*

 * This implementation of find_{first,next}_zero_bit was stolen from

 * Linus' asm-alpha/bitops.h.

 */

unsigned long find_next_zero_bit(const unsigned long *addr, unsigned long size,

		unsigned long offset)

{

	const unsigned long *p = addr + BITOP_WORD(offset);

	unsigned long result = offset & ~(BITS_PER_LONG-1);

	unsigned long tmp;



 finish:

	/* count the remaining bits without using __ffs() since that takes a 32-bit arg */

	while (!(tmp & 0xff)) {

		offset += 8;

		tmp >>= 8;

	if (offset >= size)

		return size;

	size -= result;

	offset %= BITS_PER_LONG;

	if (offset) {

		tmp = *(p++);

		tmp |= ~0UL >> (BITS_PER_LONG - offset);

		if (size < BITS_PER_LONG)

			goto found_first;

		if (~tmp)

			goto found_middle;

		size -= BITS_PER_LONG;

		result += BITS_PER_LONG;

	}



	while (!(tmp & 1)) {

		offset++;

		tmp >>= 1;

	while (size & ~(BITS_PER_LONG-1)) {

		if (~(tmp = *(p++)))

			goto found_middle;

		result += BITS_PER_LONG;

		size -= BITS_PER_LONG;

	}

	if (!size)

		return result;

	tmp = *p;



	return offset;

found_first:

	tmp |= ~0UL << size;

	if (tmp == ~0UL)	/* Are any bits zero? */

		return result + size;	/* Nope. */

found_middle:

	return result + ffz(tmp);

}



EXPORT_SYMBOL(find_next_bit);
 
EXPORT_SYMBOL(find_next_zero_bit);