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bitmap: find_last_bit()

Browse source 
Impact: New API

As the name suggests.  For the moment everyone uses the generic one.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Rusty Russell 2009-01-01 10:12:19 +10:30
parent 0db5d3d2f5
commit ab53d472e7
4 changed files with 62 additions and 1 deletions
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13
include/linux/bitops.h
View file

@ -134,9 +134,20 @@ extern unsigned long find_first_bit(const unsigned long *addr,
*/
extern unsigned long find_first_zero_bit(const unsigned long *addr,
unsigned long size);
#endif /* CONFIG_GENERIC_FIND_FIRST_BIT */
#ifdef CONFIG_GENERIC_FIND_LAST_BIT
/**
* find_last_bit - find the last set bit in a memory region
* @addr: The address to start the search at
* @size: The maximum size to search
*
* Returns the bit number of the first set bit, or size.
*/
extern unsigned long find_last_bit(const unsigned long *addr,
unsigned long size);
#endif /* CONFIG_GENERIC_FIND_LAST_BIT */
#ifdef CONFIG_GENERIC_FIND_NEXT_BIT
/**

4
lib/Kconfig
View file

@ -13,6 +13,10 @@ config GENERIC_FIND_FIRST_BIT
config GENERIC_FIND_NEXT_BIT
bool
config GENERIC_FIND_LAST_BIT
bool
default y
config CRC_CCITT
tristate "CRC-CCITT functions"
help

1
lib/Makefile
View file

@ -37,6 +37,7 @@ lib-$(CONFIG_RWSEM_GENERIC_SPINLOCK) += rwsem-spinlock.o
lib-$(CONFIG_RWSEM_XCHGADD_ALGORITHM) += rwsem.o
lib-$(CONFIG_GENERIC_FIND_FIRST_BIT) += find_next_bit.o
lib-$(CONFIG_GENERIC_FIND_NEXT_BIT) += find_next_bit.o
lib-$(CONFIG_GENERIC_FIND_LAST_BIT) += find_last_bit.o
obj-$(CONFIG_GENERIC_HWEIGHT) += hweight.o
obj-$(CONFIG_LOCK_KERNEL) += kernel_lock.o
obj-$(CONFIG_PLIST) += plist.o

45
lib/find_last_bit.c Normal file
View file

@ -0,0 +1,45 @@
/* find_last_bit.c: fallback find next bit implementation
*
* Copyright (C) 2008 IBM Corporation
* Written by Rusty Russell <rusty@rustcorp.com.au>
* (Inspired by David Howell's find_next_bit implementation)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*/
#include <linux/bitops.h>
#include <linux/module.h>
#include <asm/types.h>
#include <asm/byteorder.h>
unsigned long find_last_bit(const unsigned long *addr, unsigned long size)
{
unsigned long words;
unsigned long tmp;
/* Start at final word. */
words = size / BITS_PER_LONG;
/* Partial final word? */
if (size & (BITS_PER_LONG-1)) {
tmp = (addr[words] & (~0UL >> (BITS_PER_LONG
- (size & (BITS_PER_LONG-1)))));
if (tmp)
goto found;
}
while (words) {
tmp = addr[--words];
if (tmp) {
found:
return words * BITS_PER_LONG + __fls(tmp);
}
}
/* Not found */
return size;
}
EXPORT_SYMBOL(find_last_bit);