rfc_1982.c revision 1.1.1.1 
1/*
2 * util/rfc_1982.c - RFC 1982 Serial Number Arithmetic
3 *
4 * Copyright (c) 2023, NLnet Labs. All rights reserved.
5 *
6 * This software is open source.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
10 * are met:
11 *
12 * Redistributions of source code must retain the above copyright notice,
13 * this list of conditions and the following disclaimer.
14 *
15 * Redistributions in binary form must reproduce the above copyright notice,
16 * this list of conditions and the following disclaimer in the documentation
17 * and/or other materials provided with the distribution.
18 *
19 * Neither the name of the NLNET LABS nor the names of its contributors may
20 * be used to endorse or promote products derived from this software without
21 * specific prior written permission.
22 *
23 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
24 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
25 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
26 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
27 * HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
28 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
29 * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
30 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
31 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
32 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
33 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
34 */
35
36/**
37 * \file
38 *
39 * This file contains functions for RFC 1982 serial number arithmetic.
40 */
41#include "config.h"
42
43int
44compare_1982(uint32_t a, uint32_t b)
45{
46	/* for 32 bit values */
47	const uint32_t cutoff = ((uint32_t) 1 << (32 - 1));
48
49	if (a == b) {
50		return 0;
51	} else if ((a < b && b - a < cutoff) || (a > b && a - b > cutoff)) {
52		return -1;
53	} else {
54		return 1;
55	}
56}
57
58uint32_t
59subtract_1982(uint32_t a, uint32_t b)
60{
61	/* for 32 bit values */
62	const uint32_t cutoff = ((uint32_t) 1 << (32 - 1));
63
64	if(a == b)
65		return 0;
66	if(a < b && b - a < cutoff) {
67		return b-a;
68	}
69	if(a > b && a - b > cutoff) {
70		return ((uint32_t)0xffffffff) - (a-b-1);
71	}
72	/* wrong case, b smaller than a */
73	return 0;
74}
75