LXR linux/tools/testing/radix-tree/find_next

   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 */
  20unsigned 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
  51found_first:
  52        tmp &= (~0UL >> (BITS_PER_LONG - size));
  53        if (tmp == 0UL)         /* Are any bits set? */
  54                return result + size;   /* Nope. */
  55found_middle:
  56        return result + __ffs(tmp);
  57}
  58