source: GPL/trunk/include/linux/bitops.h

#ifndef _I386_BITOPS_H
#define _I386_BITOPS_H

#include <linux/types.h>
#include <asm/bitops.h>

/*
 * Copyright 1992, Linus Torvalds.
 */


/*
 * These have to be done with inline assembly: that way the bit-setting
 * is guaranteed to be atomic. All bit operations return 0 if the bit
 * was cleared before the operation and != 0 if it was not.
 *
 * bit 0 is the LSB of addr; bit 32 is the LSB of (addr+1).
 */

/*
 * Function prototypes to keep gcc -Wall happy
 */
#include <asm\bitops.h>
#define smp_mb__after_clear_bit()       
unsigned int hweight32(unsigned int w);
/**
 * find_first_bit - find the first set bit in a memory region
 * @addr: The address to start the search at
 * @size: The maximum number of bits to search
 *
 * Returns the bit number of the first set bit.
 * If no bits are set, returns @size.
 */
extern unsigned long find_first_bit(const unsigned long *addr,
                                    unsigned long size);


/**
 * __ffs - find first bit in word.
 * @word: The word to search
 *
 * Undefined if no bit exists, so code should check against 0 first.
 */
static inline unsigned long __ffs(unsigned long word)
{
        int num = 0;

#if BITS_PER_LONG == 64
        if ((word & 0xffffffff) == 0) {
                num += 32;
                word >>= 32;
        }
#endif
        if ((word & 0xffff) == 0) {
                num += 16;
                word >>= 16;
        }
        if ((word & 0xff) == 0) {
                num += 8;
                word >>= 8;
        }
        if ((word & 0xf) == 0) {
                num += 4;
                word >>= 4;
        }
        if ((word & 0x3) == 0) {
                num += 2;
                word >>= 2;
        }
        if ((word & 0x1) == 0)
                num += 1;
        return num;
}

/**
 * __fls - find last (most-significant) set bit in a long word
 * @word: the word to search
 *
 * Undefined if no set bit exists, so code should check against 0 first.
 */
static inline unsigned long __fls(unsigned long word)
{
        int num = BITS_PER_LONG - 1;

#if BITS_PER_LONG == 64
        if (!(word & (~0ul << 32))) {
                num -= 32;
                word <<= 32;
        }
#endif
        if (!(word & (~0ul << (BITS_PER_LONG-16)))) {
                num -= 16;
                word <<= 16;
        }
        if (!(word & (~0ul << (BITS_PER_LONG-8)))) {
                num -= 8;
                word <<= 8;
        }
        if (!(word & (~0ul << (BITS_PER_LONG-4)))) {
                num -= 4;
                word <<= 4;
        }
        if (!(word & (~0ul << (BITS_PER_LONG-2)))) {
                num -= 2;
                word <<= 2;
        }
        if (!(word & (~0ul << (BITS_PER_LONG-1))))
                num -= 1;
        return num;
}

/* same as for_each_set_bit() but use bit as value to start with */
#define for_each_set_bit_from(bit, addr, size) \
        for ((bit) = find_next_bit((addr), (size), (bit));      \
             (bit) < (size);                                    \
             (bit) = find_next_bit((addr), (size), (bit) + 1))

/**
 * fls - find last (most-significant) bit set
 * @x: the word to search
 *
 * This is defined the same way as ffs.
 * Note fls(0) = 0, fls(1) = 1, fls(0x80000000) = 32.
 */

static inline int fls(int x)
{
        int r = 32;

        if (!x)
                return 0;
        if (!(x & 0xffff0000u)) {
                x <<= 16;
                r -= 16;
        }
        if (!(x & 0xff000000u)) {
                x <<= 8;
                r -= 8;
        }
        if (!(x & 0xf0000000u)) {
                x <<= 4;
                r -= 4;
        }
        if (!(x & 0xc0000000u)) {
                x <<= 2;
                r -= 2;
        }
        if (!(x & 0x80000000u)) {
                x <<= 1;
                r -= 1;
        }
        return r;
}

#define BIT(nr)                 (1UL << (nr))
#define BIT_MASK(nr)            (1UL << ((nr) % BITS_PER_LONG))
#define BIT_WORD(nr)            ((nr) / BITS_PER_LONG)
#define BITS_PER_BYTE           8
#define BITS_TO_LONGS(nr)       DIV_ROUND_UP(nr, BITS_PER_BYTE * sizeof(long))

/*
 * Create a contiguous bitmask starting at bit position @l and ending at
 * position @h. For example
 * GENMASK_ULL(39, 21) gives us the 64bit vector 0x000000ffffe00000.
 */
#define GENMASK(h, l) \
        (((~0UL) << (l)) & (~0UL >> (BITS_PER_LONG - 1 - (h))))

#define GENMASK_ULL(h, l) \
        (((~0ULL) << (l)) & (~0ULL >> (BITS_PER_LONG_LONG - 1 - (h))))

#define for_each_set_bit(bit, addr, size) \
        for ((bit) = find_first_bit((addr), (size)); \
             (bit) < (size); \
             (bit) = find_next_bit((addr), (size), (bit) + 1))

static inline int get_bitmask_order(unsigned int count)
{
        int order;

        order = fls(count);
        return order;   /* We could be slightly more clever with -1 here... */
}

static inline int get_count_order(unsigned int count)
{
        int order;

        order = fls(count) - 1;
        if (count & (count - 1))
                order++;
        return order;
}

static inline unsigned fls_long(unsigned long l)
{
                return fls(l);
}

static inline unsigned long hweight_long(unsigned long w)
{
        return hweight32(w);
}

#endif /* _I386_BITOPS_H */