lib/bitmap.c

   1 /*
   2  * Copyright (c) 2008, 2009, 2011 Nicira, Inc.
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at:
   7  *
   8  *     http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16
  17 #include <config.h>
  18 #include "bitmap.h"
  19 #include <string.h>
  20
  21 /* Allocates and returns a bitmap initialized to all-1-bits. */
  22 unsigned long *
  23 bitmap_allocate1(size_t n_bits)
  24 {
  25     size_t n_bytes = bitmap_n_bytes(n_bits);
  26     size_t n_longs = bitmap_n_longs(n_bits);
  27     size_t r_bits = n_bits % BITMAP_ULONG_BITS;
  28     unsigned long *bitmap;
  29
  30     /* Allocate and initialize most of the bitmap. */
  31     bitmap = xmalloc(n_bytes);
  32     memset(bitmap, 0xff, n_bytes);
  33
  34     /* Ensure that the last "unsigned long" in the bitmap only has as many
  35      * 1-bits as there actually should be. */
  36     if (r_bits) {
  37         bitmap[n_longs - 1] = (1UL << r_bits) - 1;
  38     }
  39
  40     return bitmap;
  41 }
  42
  43 /* Sets 'count' consecutive bits in 'bitmap', starting at bit offset 'start',
  44  * to 'value'. */
  45 void
  46 bitmap_set_multiple(unsigned long *bitmap, size_t start, size_t count,
  47                     bool value)
  48 {
  49     for (; count && start % BITMAP_ULONG_BITS; count--) {
  50         bitmap_set(bitmap, start++, value);
  51     }
  52     for (; count >= BITMAP_ULONG_BITS; count -= BITMAP_ULONG_BITS) {
  53         *bitmap_unit__(bitmap, start) = -(unsigned long) value;
  54         start += BITMAP_ULONG_BITS;
  55     }
  56     for (; count; count--) {
  57         bitmap_set(bitmap, start++, value);
  58     }
  59 }
  60
  61 /* Compares the 'n' bits in bitmaps 'a' and 'b'.  Returns true if all bits are
  62  * equal, false otherwise. */
  63 bool
  64 bitmap_equal(const unsigned long *a, const unsigned long *b, size_t n)
  65 {
  66     size_t i;
  67
  68     if (memcmp(a, b, n / BITMAP_ULONG_BITS * sizeof(unsigned long))) {
  69         return false;
  70     }
  71     for (i = ROUND_DOWN(n, BITMAP_ULONG_BITS); i < n; i++) {
  72         if (bitmap_is_set(a, i) != bitmap_is_set(b, i)) {
  73             return false;
  74         }
  75     }
  76     return true;
  77 }
  78
  79 /* Scans 'bitmap' from bit offset 'start' to 'end', excluding 'end' itself.
  80  * Returns the bit offset of the lowest-numbered bit set to 1, or 'end' if
  81  * all of the bits are set to 0. */
  82 size_t
  83 bitmap_scan(const unsigned long int *bitmap, size_t start, size_t end)
  84 {
  85     /* XXX slow */
  86     size_t i;
  87
  88     for (i = start; i < end; i++) {
  89         if (bitmap_is_set(bitmap, i)) {
  90             break;
  91         }
  92     }
  93     return i;
  94 }