tools/lib/find_bit.c

   1 /* bit search implementation
   2  *
   3  * Copied from lib/find_bit.c to tools/lib/find_bit.c
   4  *
   5  * Copyright (C) 2004 Red Hat, Inc. All Rights Reserved.
   6  * Written by David Howells (dhowells@redhat.com)
   7  *
   8  * Copyright (C) 2008 IBM Corporation
   9  * 'find_last_bit' is written by Rusty Russell <rusty@rustcorp.com.au>
  10  * (Inspired by David Howell's find_next_bit implementation)
  11  *
  12  * Rewritten by Yury Norov <yury.norov@gmail.com> to decrease
  13  * size and improve performance, 2015.
  14  *
  15  * This program is free software; you can redistribute it and/or
  16  * modify it under the terms of the GNU General Public License
  17  * as published by the Free Software Foundation; either version
  18  * 2 of the License, or (at your option) any later version.
  19  */
  20
  21 #include <linux/bitops.h>
  22 #include <linux/bitmap.h>
  23 #include <linux/kernel.h>
  24
  25 #if !defined(find_next_bit)
  26
  27 /*
  28  * This is a common helper function for find_next_bit and
  29  * find_next_zero_bit.  The difference is the "invert" argument, which
  30  * is XORed with each fetched word before searching it for one bits.
  31  */
  32 static unsigned long _find_next_bit(const unsigned long *addr,
  33                 unsigned long nbits, unsigned long start, unsigned long invert)
  34 {
  35         unsigned long tmp;
  36
  37         if (!nbits || start >= nbits)
  38                 return nbits;
  39
  40         tmp = addr[start / BITS_PER_LONG] ^ invert;
  41
  42         /* Handle 1st word. */
  43         tmp &= BITMAP_FIRST_WORD_MASK(start);
  44         start = round_down(start, BITS_PER_LONG);
  45
  46         while (!tmp) {
  47                 start += BITS_PER_LONG;
  48                 if (start >= nbits)
  49                         return nbits;
  50
  51                 tmp = addr[start / BITS_PER_LONG] ^ invert;
  52         }
  53
  54         return min(start + __ffs(tmp), nbits);
  55 }
  56 #endif
  57
  58 #ifndef find_next_bit
  59 /*
  60  * Find the next set bit in a memory region.
  61  */
  62 unsigned long find_next_bit(const unsigned long *addr, unsigned long size,
  63                             unsigned long offset)
  64 {
  65         return _find_next_bit(addr, size, offset, 0UL);
  66 }
  67 #endif
  68
  69 #ifndef find_first_bit
  70 /*
  71  * Find the first set bit in a memory region.
  72  */
  73 unsigned long find_first_bit(const unsigned long *addr, unsigned long size)
  74 {
  75         unsigned long idx;
  76
  77         for (idx = 0; idx * BITS_PER_LONG < size; idx++) {
  78                 if (addr[idx])
  79                         return min(idx * BITS_PER_LONG + __ffs(addr[idx]), size);
  80         }
  81
  82         return size;
  83 }
  84 #endif