bitops.c

xen 3.2.2 源码

/* from linux/arch/powerpc/lib/bitops.c */

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

#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 *p = addr + BITOP_WORD(offset);
    unsigned long result = offset & ~(BITS_PER_LONG-1);
    unsigned long tmp;

    if (offset >= size)
        return size;
    size -= result;
    offset %= BITS_PER_LONG;
    if (offset) {
        tmp = *(p++);
        tmp &= (~0UL << offset);
        if (size < BITS_PER_LONG)
            goto found_first;
        if (tmp)
            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;

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);
}

/*
 * 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;

    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 (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;

found_first:
    tmp |= ~0UL << size;
    if (tmp == ~0UL)    /* Are any bits zero? */
        return result + size;    /* Nope. */
found_middle:
    return result + ffz(tmp);
}