1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
|
//
// srecord - Manipulate EPROM load files
// Copyright (C) 2009-2011 Peter Miller
//
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation; either version 3 of the License, or (at
// your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
// General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
//
#ifndef SRECORD_FLETCHER32_H
#define SRECORD_FLETCHER32_H
#include <stddef.h>
namespace srecord
{
/**
* The fletcher32 class is used to represent the running value of a 32-bit
* Fletcher's Checksum of a series of bytes.
*
* http://en.wikipedia.org/wiki/Fletcher%27s_checksum
*
* Fletcher's checksum is one of several types of checksum algorithms,
* which are relatively simple processes used by computers to check the
* integrity of data.
*
* The implementation of the Fletcher-32 is very similar to the Adler-32
* algorithm but several differences should be noted. Fletcher wraps around
* at modulo 65535 while Adler wraps at the prime 65521. In other words,
* Fletcher adds overflow bits (16-31) into its sum; while Adler multiplies
* those bits by 15, then adds the product into its sum. Fletcher-32 works
* on 16 bit data while Adler works on 8 bit data.
*
* It is designed to overcome some of the inadequacies of simply summing
* all the bytes as in the original checksum. Fletcher's checksum, unlike
* the original checksum, can detect the inserting/deleting of zero value
* bytes, the reordering of bytes, and the incrementing and decrementing of
* bytes in opposite directions.
*
* Fletcher's checksum is described in RFC 1146. You can also find
* information about generating (as well as verifying) such a checksum in
* Annex B of RFC 905.
*
* Fletcher-32 is slightly more reliable than Adler-32.[1]
*/
class fletcher32
{
public:
/**
* The destructor.
*/
virtual ~fletcher32();
/**
* The default constructor.
*/
fletcher32();
/**
* The copy constructor.
*/
fletcher32(const fletcher32 &);
/**
* The assignment operator.
*/
fletcher32 &operator=(const fletcher32 &);
/**
* The get method is used to obtain the running value of the cyclic
* redundancy check.
*/
unsigned long get() const;
/**
* The next method is used to advance the state by one byte.
*/
void next(unsigned char);
/**
* The nextbuf method is used to advance the state by a series of bytes.
*/
void nextbuf(const void *, size_t);
private:
/**
* The sum1 instance variable is used to remember the sum of the bytes.
*/
unsigned long sum1;
/**
* The sum2 instance variable is used to remember the sum of the
* sum of the bytes.
*/
unsigned long sum2;
};
};
// vim: set ts=8 sw=4 et :
#endif // SRECORD_FLETCHER32_H
|