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
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
|
/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* Copyright by the Board of Trustees of the University of Illinois. *
* All rights reserved. *
* *
* This file is part of HDF5. The full HDF5 copyright notice, including *
* terms governing use, modification, and redistribution, is contained in *
* the files COPYING and Copyright.html. COPYING can be found at the root *
* of the source code distribution tree; Copyright.html can be found at the *
* root level of an installed copy of the electronic HDF5 document set and *
* is linked from the top-level documents page. It can also be found at *
* http://hdf.ncsa.uiuc.edu/HDF5/doc/Copyright.html. If you do not have *
* access to either file, you may request a copy from hdfhelp@ncsa.uiuc.edu. *
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
/*-------------------------------------------------------------------------
*
* Created: H5checksum.c
* Aug 21 2006
* Quincey Koziol <koziol@hdfgroup.org>
*
* Purpose: Internal code for computing fletcher32 checksums
*
*-------------------------------------------------------------------------
*/
/****************/
/* Module Setup */
/****************/
/***********/
/* Headers */
/***********/
#include "H5private.h" /* Generic Functions */
/****************/
/* Local Macros */
/****************/
/******************/
/* Local Typedefs */
/******************/
/********************/
/* Package Typedefs */
/********************/
/********************/
/* Local Prototypes */
/********************/
/*********************/
/* Package Variables */
/*********************/
/*****************************/
/* Library Private Variables */
/*****************************/
/*******************/
/* Local Variables */
/*******************/
/*-------------------------------------------------------------------------
* Function: H5_fletcher32
*
* Purpose: This routine provides a generic, fast checksum algorithm for
* use in the library.
*
* Note: See the Wikipedia page for Fletcher's checksum:
* http://en.wikipedia.org/wiki/Fletcher%27s_checksum
* for more details, etc.
*
* Note #2: The algorithm below differs from that given in the Wikipedia
* page by copying the data into 'sum1' in a more portable way
* and also by initializing 'sum1' and 'sum2' to 0 instead of
* 0xffff (for backward compatibility reasons, mostly).
*
* Return: 32-bit fletcher checksum of input buffer (can't fail)
*
* Programmer: Quincey Koziol
* Monday, August 21, 2006
*
*-------------------------------------------------------------------------
*/
uint32_t
H5_fletcher32(const void *_data, size_t _len)
{
const uint8_t *data = (const uint8_t *)_data; /* Pointer to the data to be summed */
size_t len = _len / 2; /* Length in 16-bit words */
uint32_t sum1 = 0, sum2 = 0;
FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5_fletcher32)
/* Sanity check */
HDassert(_data);
HDassert(_len > 0);
/* Compute checksum for pairs of bytes */
/* (the magic "360" value is is the largest number of sums that can be
* performed without numeric overflow)
*/
while (len) {
unsigned tlen = len > 360 ? 360 : len;
len -= tlen;
do {
sum1 += (((uint16_t)data[0]) << 8) | ((uint16_t)data[1]);
data += 2;
sum2 += sum1;
} while (--tlen);
sum1 = (sum1 & 0xffff) + (sum1 >> 16);
sum2 = (sum2 & 0xffff) + (sum2 >> 16);
}
/* Check for odd # of bytes */
if(_len % 2) {
sum1 += ((uint16_t)*data) << 8;
sum2 += sum1;
sum1 = (sum1 & 0xffff) + (sum1 >> 16);
sum2 = (sum2 & 0xffff) + (sum2 >> 16);
} /* end if */
/* Second reduction step to reduce sums to 16 bits */
sum1 = (sum1 & 0xffff) + (sum1 >> 16);
sum2 = (sum2 & 0xffff) + (sum2 >> 16);
FUNC_LEAVE_NOAPI((sum2 << 16) | sum1)
} /* end H5_fletcher32() */
/*-------------------------------------------------------------------------
* Function: H5_checksum_metadata
*
* Purpose: Provide a more abstract routine for checksumming metadata
* in a file, where the policy of which algorithm to choose
* is centralized.
*
* Return: checksum of input buffer (can't fail)
*
* Programmer: Quincey Koziol
* Tuesday, August 22, 2006
*
*-------------------------------------------------------------------------
*/
uint32_t
H5_checksum_metadata(const void *data, size_t len)
{
uint32_t chksum; /* Checksum value to return */
FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5_checksum_metadata)
/* Sanity check */
HDassert(data);
HDassert(len > 0);
/* Choose the appropriate checksum routine */
/* (use fletcher32 for everything right now, but will probably go
* with a CRC algorithm for "shorter" pieces of metadata eventually)
*/
chksum = H5_fletcher32(data, len);
FUNC_LEAVE_NOAPI(chksum)
} /* end H5_checksum_metadata() */
|
