tools/testing/radix-tree/find_next_bit.c

   1 /* find_next_bit.c: fallback find next bit implementation
   2  *
   3  * Copyright (C) 2004 Red Hat, Inc. All Rights Reserved.
   4  * Written by David Howells (dhowells@redhat.com)
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public License
   8  * as published by the Free Software Foundation; either version
   9  * 2 of the License, or (at your option) any later version.
  10  */
  11
  12 #include <linux/types.h>
  13 #include <linux/bitops.h>
  14
  15 #define BITOP_WORD(nr)          ((nr) / BITS_PER_LONG)
  16
  17 /*
  18  * Find the next set bit in a memory region.
  19  */
  20 unsigned long find_next_bit(const unsigned long *addr, unsigned long size,
  21                             unsigned long offset)
  22 {
  23         const unsigned long *p = addr + BITOP_WORD(offset);
  24         unsigned long result = offset & ~(BITS_PER_LONG-1);
  25         unsigned long tmp;
  26
  27         if (offset >= size)
  28                 return size;
  29         size -= result;
  30         offset %= BITS_PER_LONG;
  31         if (offset) {
  32                 tmp = *(p++);
  33                 tmp &= (~0UL << offset);
  34                 if (size < BITS_PER_LONG)
  35                         goto found_first;
  36                 if (tmp)
  37                         goto found_middle;
  38                 size -= BITS_PER_LONG;
  39                 result += BITS_PER_LONG;
  40         }
  41         while (size & ~(BITS_PER_LONG-1)) {
  42                 if ((tmp = *(p++)))
  43                         goto found_middle;
  44                 result += BITS_PER_LONG;
  45                 size -= BITS_PER_LONG;
  46         }
  47         if (!size)
  48                 return result;
  49         tmp = *p;
  50
  51 found_first:
  52         tmp &= (~0UL >> (BITS_PER_LONG - size));
  53         if (tmp == 0UL)         /* Are any bits set? */
  54                 return result + size;   /* Nope. */
  55 found_middle:
  56         return result + __ffs(tmp);
  57 }