lib/find_bit.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /* bit search implementation
   3  *
   4  * Copyright (C) 2004 Red Hat, Inc. All Rights Reserved.
   5  * Written by David Howells (dhowells@redhat.com)
   6  *
   7  * Copyright (C) 2008 IBM Corporation
   8  * 'find_last_bit' is written by Rusty Russell <rusty@rustcorp.com.au>
   9  * (Inspired by David Howell's find_next_bit implementation)
  10  *
  11  * Rewritten by Yury Norov <yury.norov@gmail.com> to decrease
  12  * size and improve performance, 2015.
  13  */
  14
  15 #include <linux/bitops.h>
  16 #include <linux/bitmap.h>
  17 #include <linux/export.h>
  18 #include <linux/math.h>
  19 #include <linux/minmax.h>
  20 #include <linux/swab.h>
  21
  22 #if !defined(find_next_bit) || !defined(find_next_zero_bit) ||                  \
  23         !defined(find_next_bit_le) || !defined(find_next_zero_bit_le) ||        \
  24         !defined(find_next_and_bit)
  25 /*
  26  * This is a common helper function for find_next_bit, find_next_zero_bit, and
  27  * find_next_and_bit. The differences are:
  28  *  - The "invert" argument, which is XORed with each fetched word before
  29  *    searching it for one bits.
  30  *  - The optional "addr2", which is anded with "addr1" if present.
  31  */
  32 unsigned long _find_next_bit(const unsigned long *addr1,
  33                 const unsigned long *addr2, unsigned long nbits,
  34                 unsigned long start, unsigned long invert, unsigned long le)
  35 {
  36         unsigned long tmp, mask;
  37
  38         if (unlikely(start >= nbits))
  39                 return nbits;
  40
  41         tmp = addr1[start / BITS_PER_LONG];
  42         if (addr2)
  43                 tmp &= addr2[start / BITS_PER_LONG];
  44         tmp ^= invert;
  45
  46         /* Handle 1st word. */
  47         mask = BITMAP_FIRST_WORD_MASK(start);
  48         if (le)
  49                 mask = swab(mask);
  50
  51         tmp &= mask;
  52
  53         start = round_down(start, BITS_PER_LONG);
  54
  55         while (!tmp) {
  56                 start += BITS_PER_LONG;
  57                 if (start >= nbits)
  58                         return nbits;
  59
  60                 tmp = addr1[start / BITS_PER_LONG];
  61                 if (addr2)
  62                         tmp &= addr2[start / BITS_PER_LONG];
  63                 tmp ^= invert;
  64         }
  65
  66         if (le)
  67                 tmp = swab(tmp);
  68
  69         return min(start + __ffs(tmp), nbits);
  70 }
  71 EXPORT_SYMBOL(_find_next_bit);
  72 #endif
  73
  74 #ifndef find_first_bit
  75 /*
  76  * Find the first set bit in a memory region.
  77  */
  78 unsigned long _find_first_bit(const unsigned long *addr, unsigned long size)
  79 {
  80         unsigned long idx;
  81
  82         for (idx = 0; idx * BITS_PER_LONG < size; idx++) {
  83                 if (addr[idx])
  84                         return min(idx * BITS_PER_LONG + __ffs(addr[idx]), size);
  85         }
  86
  87         return size;
  88 }
  89 EXPORT_SYMBOL(_find_first_bit);
  90 #endif
  91
  92 #ifndef find_first_zero_bit
  93 /*
  94  * Find the first cleared bit in a memory region.
  95  */
  96 unsigned long _find_first_zero_bit(const unsigned long *addr, unsigned long size)
  97 {
  98         unsigned long idx;
  99
 100         for (idx = 0; idx * BITS_PER_LONG < size; idx++) {
 101                 if (addr[idx] != ~0UL)
 102                         return min(idx * BITS_PER_LONG + ffz(addr[idx]), size);
 103         }
 104
 105         return size;
 106 }
 107 EXPORT_SYMBOL(_find_first_zero_bit);
 108 #endif
 109
 110 #ifndef find_last_bit
 111 unsigned long _find_last_bit(const unsigned long *addr, unsigned long size)
 112 {
 113         if (size) {
 114                 unsigned long val = BITMAP_LAST_WORD_MASK(size);
 115                 unsigned long idx = (size-1) / BITS_PER_LONG;
 116
 117                 do {
 118                         val &= addr[idx];
 119                         if (val)
 120                                 return idx * BITS_PER_LONG + __fls(val);
 121
 122                         val = ~0ul;
 123                 } while (idx--);
 124         }
 125         return size;
 126 }
 127 EXPORT_SYMBOL(_find_last_bit);
 128 #endif
 129
 130 unsigned long find_next_clump8(unsigned long *clump, const unsigned long *addr,
 131                                unsigned long size, unsigned long offset)
 132 {
 133         offset = find_next_bit(addr, size, offset);
 134         if (offset == size)
 135                 return size;
 136
 137         offset = round_down(offset, 8);
 138         *clump = bitmap_get_value8(addr, offset);
 139
 140         return offset;
 141 }
 142 EXPORT_SYMBOL(find_next_clump8);