fs/xfs/libxfs/xfs_bit.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright (c) 2000-2005 Silicon Graphics, Inc.
   4  * All Rights Reserved.
   5  */
   6 #include "xfs.h"
   7 #include "xfs_log_format.h"
   8 #include "xfs_bit.h"
   9
  10 /*
  11  * XFS bit manipulation routines, used in non-realtime code.
  12  */
  13
  14 /*
  15  * Return whether bitmap is empty.
  16  * Size is number of words in the bitmap, which is padded to word boundary
  17  * Returns 1 for empty, 0 for non-empty.
  18  */
  19 int
  20 xfs_bitmap_empty(uint *map, uint size)
  21 {
  22         uint i;
  23
  24         for (i = 0; i < size; i++) {
  25                 if (map[i] != 0)
  26                         return 0;
  27         }
  28
  29         return 1;
  30 }
  31
  32 /*
  33  * Count the number of contiguous bits set in the bitmap starting with bit
  34  * start_bit.  Size is the size of the bitmap in words.
  35  */
  36 int
  37 xfs_contig_bits(uint *map, uint size, uint start_bit)
  38 {
  39         uint * p = ((unsigned int *) map) + (start_bit >> BIT_TO_WORD_SHIFT);
  40         uint result = 0;
  41         uint tmp;
  42
  43         size <<= BIT_TO_WORD_SHIFT;
  44
  45         ASSERT(start_bit < size);
  46         size -= start_bit & ~(NBWORD - 1);
  47         start_bit &= (NBWORD - 1);
  48         if (start_bit) {
  49                 tmp = *p++;
  50                 /* set to one first offset bits prior to start */
  51                 tmp |= (~0U >> (NBWORD-start_bit));
  52                 if (tmp != ~0U)
  53                         goto found;
  54                 result += NBWORD;
  55                 size -= NBWORD;
  56         }
  57         while (size) {
  58                 if ((tmp = *p++) != ~0U)
  59                         goto found;
  60                 result += NBWORD;
  61                 size -= NBWORD;
  62         }
  63         return result - start_bit;
  64 found:
  65         return result + ffz(tmp) - start_bit;
  66 }
  67
  68 /*
  69  * This takes the bit number to start looking from and
  70  * returns the next set bit from there.  It returns -1
  71  * if there are no more bits set or the start bit is
  72  * beyond the end of the bitmap.
  73  *
  74  * Size is the number of words, not bytes, in the bitmap.
  75  */
  76 int xfs_next_bit(uint *map, uint size, uint start_bit)
  77 {
  78         uint * p = ((unsigned int *) map) + (start_bit >> BIT_TO_WORD_SHIFT);
  79         uint result = start_bit & ~(NBWORD - 1);
  80         uint tmp;
  81
  82         size <<= BIT_TO_WORD_SHIFT;
  83
  84         if (start_bit >= size)
  85                 return -1;
  86         size -= result;
  87         start_bit &= (NBWORD - 1);
  88         if (start_bit) {
  89                 tmp = *p++;
  90                 /* set to zero first offset bits prior to start */
  91                 tmp &= (~0U << start_bit);
  92                 if (tmp != 0U)
  93                         goto found;
  94                 result += NBWORD;
  95                 size -= NBWORD;
  96         }
  97         while (size) {
  98                 if ((tmp = *p++) != 0U)
  99                         goto found;
 100                 result += NBWORD;
 101                 size -= NBWORD;
 102         }
 103         return -1;
 104 found:
 105         return result + ffs(tmp) - 1;
 106 }