fs/xfs/xfs_bit.c

   1 /*
   2  * Copyright (c) 2000-2005 Silicon Graphics, Inc.
   3  * All Rights Reserved.
   4  *
   5  * This program is free software; you can redistribute it and/or
   6  * modify it under the terms of the GNU General Public License as
   7  * published by the Free Software Foundation.
   8  *
   9  * This program is distributed in the hope that it would be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, write the Free Software Foundation,
  16  * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  17  */
  18 #include "xfs.h"
  19 #include "xfs_bit.h"
  20 #include "xfs_log.h"
  21 #include "xfs_trans.h"
  22 #include "xfs_buf_item.h"
  23
  24 /*
  25  * XFS bit manipulation routines, used in non-realtime code.
  26  */
  27
  28 /*
  29  * Return whether bitmap is empty.
  30  * Size is number of words in the bitmap, which is padded to word boundary
  31  * Returns 1 for empty, 0 for non-empty.
  32  */
  33 int
  34 xfs_bitmap_empty(uint *map, uint size)
  35 {
  36         uint i;
  37         uint ret = 0;
  38
  39         for (i = 0; i < size; i++) {
  40                 ret |= map[i];
  41         }
  42
  43         return (ret == 0);
  44 }
  45
  46 /*
  47  * Count the number of contiguous bits set in the bitmap starting with bit
  48  * start_bit.  Size is the size of the bitmap in words.
  49  */
  50 int
  51 xfs_contig_bits(uint *map, uint size, uint start_bit)
  52 {
  53         uint * p = ((unsigned int *) map) + (start_bit >> BIT_TO_WORD_SHIFT);
  54         uint result = 0;
  55         uint tmp;
  56
  57         size <<= BIT_TO_WORD_SHIFT;
  58
  59         ASSERT(start_bit < size);
  60         size -= start_bit & ~(NBWORD - 1);
  61         start_bit &= (NBWORD - 1);
  62         if (start_bit) {
  63                 tmp = *p++;
  64                 /* set to one first offset bits prior to start */
  65                 tmp |= (~0U >> (NBWORD-start_bit));
  66                 if (tmp != ~0U)
  67                         goto found;
  68                 result += NBWORD;
  69                 size -= NBWORD;
  70         }
  71         while (size) {
  72                 if ((tmp = *p++) != ~0U)
  73                         goto found;
  74                 result += NBWORD;
  75                 size -= NBWORD;
  76         }
  77         return result - start_bit;
  78 found:
  79         return result + ffz(tmp) - start_bit;
  80 }
  81
  82 /*
  83  * This takes the bit number to start looking from and
  84  * returns the next set bit from there.  It returns -1
  85  * if there are no more bits set or the start bit is
  86  * beyond the end of the bitmap.
  87  *
  88  * Size is the number of words, not bytes, in the bitmap.
  89  */
  90 int xfs_next_bit(uint *map, uint size, uint start_bit)
  91 {
  92         uint * p = ((unsigned int *) map) + (start_bit >> BIT_TO_WORD_SHIFT);
  93         uint result = start_bit & ~(NBWORD - 1);
  94         uint tmp;
  95
  96         size <<= BIT_TO_WORD_SHIFT;
  97
  98         if (start_bit >= size)
  99                 return -1;
 100         size -= result;
 101         start_bit &= (NBWORD - 1);
 102         if (start_bit) {
 103                 tmp = *p++;
 104                 /* set to zero first offset bits prior to start */
 105                 tmp &= (~0U << start_bit);
 106                 if (tmp != 0U)
 107                         goto found;
 108                 result += NBWORD;
 109                 size -= NBWORD;
 110         }
 111         while (size) {
 112                 if ((tmp = *p++) != 0U)
 113                         goto found;
 114                 result += NBWORD;
 115                 size -= NBWORD;
 116         }
 117         return -1;
 118 found:
 119         return result + ffs(tmp) - 1;
 120 }