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_log_format.h"
  20 #include "xfs_bit.h"
  21
  22 /*
  23  * XFS bit manipulation routines, used in non-realtime code.
  24  */
  25
  26 /*
  27  * Return whether bitmap is empty.
  28  * Size is number of words in the bitmap, which is padded to word boundary
  29  * Returns 1 for empty, 0 for non-empty.
  30  */
  31 int
  32 xfs_bitmap_empty(uint *map, uint size)
  33 {
  34         uint i;
  35         uint ret = 0;
  36
  37         for (i = 0; i < size; i++) {
  38                 ret |= map[i];
  39         }
  40
  41         return (ret == 0);
  42 }
  43
  44 /*
  45  * Count the number of contiguous bits set in the bitmap starting with bit
  46  * start_bit.  Size is the size of the bitmap in words.
  47  */
  48 int
  49 xfs_contig_bits(uint *map, uint size, uint start_bit)
  50 {
  51         uint * p = ((unsigned int *) map) + (start_bit >> BIT_TO_WORD_SHIFT);
  52         uint result = 0;
  53         uint tmp;
  54
  55         size <<= BIT_TO_WORD_SHIFT;
  56
  57         ASSERT(start_bit < size);
  58         size -= start_bit & ~(NBWORD - 1);
  59         start_bit &= (NBWORD - 1);
  60         if (start_bit) {
  61                 tmp = *p++;
  62                 /* set to one first offset bits prior to start */
  63                 tmp |= (~0U >> (NBWORD-start_bit));
  64                 if (tmp != ~0U)
  65                         goto found;
  66                 result += NBWORD;
  67                 size -= NBWORD;
  68         }
  69         while (size) {
  70                 if ((tmp = *p++) != ~0U)
  71                         goto found;
  72                 result += NBWORD;
  73                 size -= NBWORD;
  74         }
  75         return result - start_bit;
  76 found:
  77         return result + ffz(tmp) - start_bit;
  78 }
  79
  80 /*
  81  * This takes the bit number to start looking from and
  82  * returns the next set bit from there.  It returns -1
  83  * if there are no more bits set or the start bit is
  84  * beyond the end of the bitmap.
  85  *
  86  * Size is the number of words, not bytes, in the bitmap.
  87  */
  88 int xfs_next_bit(uint *map, uint size, uint start_bit)
  89 {
  90         uint * p = ((unsigned int *) map) + (start_bit >> BIT_TO_WORD_SHIFT);
  91         uint result = start_bit & ~(NBWORD - 1);
  92         uint tmp;
  93
  94         size <<= BIT_TO_WORD_SHIFT;
  95
  96         if (start_bit >= size)
  97                 return -1;
  98         size -= result;
  99         start_bit &= (NBWORD - 1);
 100         if (start_bit) {
 101                 tmp = *p++;
 102                 /* set to zero first offset bits prior to start */
 103                 tmp &= (~0U << start_bit);
 104                 if (tmp != 0U)
 105                         goto found;
 106                 result += NBWORD;
 107                 size -= NBWORD;
 108         }
 109         while (size) {
 110                 if ((tmp = *p++) != 0U)
 111                         goto found;
 112                 result += NBWORD;
 113                 size -= NBWORD;
 114         }
 115         return -1;
 116 found:
 117         return result + ffs(tmp) - 1;
 118 }