root/fs/xfs/xfs_bit.c

DEFINITIONS

1. xfs_bitmap_empty
2. xfs_contig_bits
3. xfs_next_bit

/*
 * Copyright (c) 2000-2005 Silicon Graphics, Inc.
 * All Rights Reserved.
 *
 * 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.
 *
 * This program is distributed in the hope that it would be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write the Free Software Foundation,
 * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
#include "xfs.h"
#include "xfs_bit.h"
#include "xfs_log.h"
#include "xfs_trans.h"
#include "xfs_buf_item.h"

/*
 * XFS bit manipulation routines, used in non-realtime code.
 */

/*
 * Return whether bitmap is empty.
 * Size is number of words in the bitmap, which is padded to word boundary
 * Returns 1 for empty, 0 for non-empty.
 */
int
xfs_bitmap_empty(uint *map, uint size)
{
        uint i;
        uint ret = 0;

        for (i = 0; i < size; i++) {
                ret |= map[i];
        }

        return (ret == 0);
}

/*
 * Count the number of contiguous bits set in the bitmap starting with bit
 * start_bit.  Size is the size of the bitmap in words.
 */
int
xfs_contig_bits(uint *map, uint size, uint start_bit)
{
        uint * p = ((unsigned int *) map) + (start_bit >> BIT_TO_WORD_SHIFT);
        uint result = 0;
        uint tmp;

        size <<= BIT_TO_WORD_SHIFT;

        ASSERT(start_bit < size);
        size -= start_bit & ~(NBWORD - 1);
        start_bit &= (NBWORD - 1);
        if (start_bit) {
                tmp = *p++;
                /* set to one first offset bits prior to start */
                tmp |= (~0U >> (NBWORD-start_bit));
                if (tmp != ~0U)
                        goto found;
                result += NBWORD;
                size -= NBWORD;
        }
        while (size) {
                if ((tmp = *p++) != ~0U)
                        goto found;
                result += NBWORD;
                size -= NBWORD;
        }
        return result - start_bit;
found:
        return result + ffz(tmp) - start_bit;
}

/*
 * This takes the bit number to start looking from and
 * returns the next set bit from there.  It returns -1
 * if there are no more bits set or the start bit is
 * beyond the end of the bitmap.
 *
 * Size is the number of words, not bytes, in the bitmap.
 */
int xfs_next_bit(uint *map, uint size, uint start_bit)
{
        uint * p = ((unsigned int *) map) + (start_bit >> BIT_TO_WORD_SHIFT);
        uint result = start_bit & ~(NBWORD - 1);
        uint tmp;

        size <<= BIT_TO_WORD_SHIFT;

        if (start_bit >= size)
                return -1;
        size -= result;
        start_bit &= (NBWORD - 1);
        if (start_bit) {
                tmp = *p++;
                /* set to zero first offset bits prior to start */
                tmp &= (~0U << start_bit);
                if (tmp != 0U)
                        goto found;
                result += NBWORD;
                size -= NBWORD;
        }
        while (size) {
                if ((tmp = *p++) != 0U)
                        goto found;
                result += NBWORD;
                size -= NBWORD;
        }
        return -1;
found:
        return result + ffs(tmp) - 1;
}