lib/find_last_bit.c

   1 /* find_last_bit.c: fallback find next bit implementation
   2  *
   3  * Copyright (C) 2008 IBM Corporation
   4  * Written by Rusty Russell <rusty@rustcorp.com.au>
   5  * (Inspired by David Howell's find_next_bit implementation)
   6  *
   7  * This program is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU General Public License
   9  * as published by the Free Software Foundation; either version
  10  * 2 of the License, or (at your option) any later version.
  11  */
  12
  13 #include <linux/bitops.h>
  14 #include <linux/module.h>
  15 #include <asm/types.h>
  16 #include <asm/byteorder.h>
  17
  18 unsigned long find_last_bit(const unsigned long *addr, unsigned long size)
  19 {
  20         unsigned long words;
  21         unsigned long tmp;
  22
  23         /* Start at final word. */
  24         words = size / BITS_PER_LONG;
  25
  26         /* Partial final word? */
  27         if (size & (BITS_PER_LONG-1)) {
  28                 tmp = (addr[words] & (~0UL >> (BITS_PER_LONG
  29                                          - (size & (BITS_PER_LONG-1)))));
  30                 if (tmp)
  31                         goto found;
  32         }
  33
  34         while (words) {
  35                 tmp = addr[--words];
  36                 if (tmp) {
  37 found:
  38                         return words * BITS_PER_LONG + __fls(tmp);
  39                 }
  40         }
  41
  42         /* Not found */
  43         return size;
  44 }
  45 EXPORT_SYMBOL(find_last_bit);