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
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
|
#include "vt.h"
#include "hamm.h"
// table to decode hamm8/4 encoded bytes.
// the low 4 bits are the (corrected) data bits
// bit 8 is set if there was a single bit error
// bit 12 is set if there was an uncorrectable error
// the idea: you may add up to 15 words and get the
// number of single bit errors in b8-b11 and the number
// of double errors in b12-b15
static unsigned short hammtab[256] =
{
0x0101, 0x100f, 0x0001, 0x0101, 0x100f, 0x0100, 0x0101, 0x100f,
0x100f, 0x0102, 0x0101, 0x100f, 0x010a, 0x100f, 0x100f, 0x0107,
0x100f, 0x0100, 0x0101, 0x100f, 0x0100, 0x0000, 0x100f, 0x0100,
0x0106, 0x100f, 0x100f, 0x010b, 0x100f, 0x0100, 0x0103, 0x100f,
0x100f, 0x010c, 0x0101, 0x100f, 0x0104, 0x100f, 0x100f, 0x0107,
0x0106, 0x100f, 0x100f, 0x0107, 0x100f, 0x0107, 0x0107, 0x0007,
0x0106, 0x100f, 0x100f, 0x0105, 0x100f, 0x0100, 0x010d, 0x100f,
0x0006, 0x0106, 0x0106, 0x100f, 0x0106, 0x100f, 0x100f, 0x0107,
0x100f, 0x0102, 0x0101, 0x100f, 0x0104, 0x100f, 0x100f, 0x0109,
0x0102, 0x0002, 0x100f, 0x0102, 0x100f, 0x0102, 0x0103, 0x100f,
0x0108, 0x100f, 0x100f, 0x0105, 0x100f, 0x0100, 0x0103, 0x100f,
0x100f, 0x0102, 0x0103, 0x100f, 0x0103, 0x100f, 0x0003, 0x0103,
0x0104, 0x100f, 0x100f, 0x0105, 0x0004, 0x0104, 0x0104, 0x100f,
0x100f, 0x0102, 0x010f, 0x100f, 0x0104, 0x100f, 0x100f, 0x0107,
0x100f, 0x0105, 0x0105, 0x0005, 0x0104, 0x100f, 0x100f, 0x0105,
0x0106, 0x100f, 0x100f, 0x0105, 0x100f, 0x010e, 0x0103, 0x100f,
0x100f, 0x010c, 0x0101, 0x100f, 0x010a, 0x100f, 0x100f, 0x0109,
0x010a, 0x100f, 0x100f, 0x010b, 0x000a, 0x010a, 0x010a, 0x100f,
0x0108, 0x100f, 0x100f, 0x010b, 0x100f, 0x0100, 0x010d, 0x100f,
0x100f, 0x010b, 0x010b, 0x000b, 0x010a, 0x100f, 0x100f, 0x010b,
0x010c, 0x000c, 0x100f, 0x010c, 0x100f, 0x010c, 0x010d, 0x100f,
0x100f, 0x010c, 0x010f, 0x100f, 0x010a, 0x100f, 0x100f, 0x0107,
0x100f, 0x010c, 0x010d, 0x100f, 0x010d, 0x100f, 0x000d, 0x010d,
0x0106, 0x100f, 0x100f, 0x010b, 0x100f, 0x010e, 0x010d, 0x100f,
0x0108, 0x100f, 0x100f, 0x0109, 0x100f, 0x0109, 0x0109, 0x0009,
0x100f, 0x0102, 0x010f, 0x100f, 0x010a, 0x100f, 0x100f, 0x0109,
0x0008, 0x0108, 0x0108, 0x100f, 0x0108, 0x100f, 0x100f, 0x0109,
0x0108, 0x100f, 0x100f, 0x010b, 0x100f, 0x010e, 0x0103, 0x100f,
0x100f, 0x010c, 0x010f, 0x100f, 0x0104, 0x100f, 0x100f, 0x0109,
0x010f, 0x100f, 0x000f, 0x010f, 0x100f, 0x010e, 0x010f, 0x100f,
0x0108, 0x100f, 0x100f, 0x0105, 0x100f, 0x010e, 0x010d, 0x100f,
0x100f, 0x010e, 0x010f, 0x100f, 0x010e, 0x000e, 0x100f, 0x010e,
};
#if 0 // this information is contained in hamm24par bit 5
// simple parity table (sum of 1 bits modulo 2)
static char odd_parity[256] =
{
0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0
};
#endif
// this table generates the parity checks for hamm24/18 decoding.
// bit 0 is for test A, 1 for B, ...
// thanks to R. Gancarz for this fine table *g*
static char hamm24par[3][256] =
{
{ // parities of first byte
0, 33, 34, 3, 35, 2, 1, 32, 36, 5, 6, 39, 7, 38, 37, 4,
37, 4, 7, 38, 6, 39, 36, 5, 1, 32, 35, 2, 34, 3, 0, 33,
38, 7, 4, 37, 5, 36, 39, 6, 2, 35, 32, 1, 33, 0, 3, 34,
3, 34, 33, 0, 32, 1, 2, 35, 39, 6, 5, 36, 4, 37, 38, 7,
39, 6, 5, 36, 4, 37, 38, 7, 3, 34, 33, 0, 32, 1, 2, 35,
2, 35, 32, 1, 33, 0, 3, 34, 38, 7, 4, 37, 5, 36, 39, 6,
1, 32, 35, 2, 34, 3, 0, 33, 37, 4, 7, 38, 6, 39, 36, 5,
36, 5, 6, 39, 7, 38, 37, 4, 0, 33, 34, 3, 35, 2, 1, 32,
40, 9, 10, 43, 11, 42, 41, 8, 12, 45, 46, 15, 47, 14, 13, 44,
13, 44, 47, 14, 46, 15, 12, 45, 41, 8, 11, 42, 10, 43, 40, 9,
14, 47, 44, 13, 45, 12, 15, 46, 42, 11, 8, 41, 9, 40, 43, 10,
43, 10, 9, 40, 8, 41, 42, 11, 15, 46, 45, 12, 44, 13, 14, 47,
15, 46, 45, 12, 44, 13, 14, 47, 43, 10, 9, 40, 8, 41, 42, 11,
42, 11, 8, 41, 9, 40, 43, 10, 14, 47, 44, 13, 45, 12, 15, 46,
41, 8, 11, 42, 10, 43, 40, 9, 13, 44, 47, 14, 46, 15, 12, 45,
12, 45, 46, 15, 47, 14, 13, 44, 40, 9, 10, 43, 11, 42, 41, 8
}, { // parities of second byte
0, 41, 42, 3, 43, 2, 1, 40, 44, 5, 6, 47, 7, 46, 45, 4,
45, 4, 7, 46, 6, 47, 44, 5, 1, 40, 43, 2, 42, 3, 0, 41,
46, 7, 4, 45, 5, 44, 47, 6, 2, 43, 40, 1, 41, 0, 3, 42,
3, 42, 41, 0, 40, 1, 2, 43, 47, 6, 5, 44, 4, 45, 46, 7,
47, 6, 5, 44, 4, 45, 46, 7, 3, 42, 41, 0, 40, 1, 2, 43,
2, 43, 40, 1, 41, 0, 3, 42, 46, 7, 4, 45, 5, 44, 47, 6,
1, 40, 43, 2, 42, 3, 0, 41, 45, 4, 7, 46, 6, 47, 44, 5,
44, 5, 6, 47, 7, 46, 45, 4, 0, 41, 42, 3, 43, 2, 1, 40,
48, 25, 26, 51, 27, 50, 49, 24, 28, 53, 54, 31, 55, 30, 29, 52,
29, 52, 55, 30, 54, 31, 28, 53, 49, 24, 27, 50, 26, 51, 48, 25,
30, 55, 52, 29, 53, 28, 31, 54, 50, 27, 24, 49, 25, 48, 51, 26,
51, 26, 25, 48, 24, 49, 50, 27, 31, 54, 53, 28, 52, 29, 30, 55,
31, 54, 53, 28, 52, 29, 30, 55, 51, 26, 25, 48, 24, 49, 50, 27,
50, 27, 24, 49, 25, 48, 51, 26, 30, 55, 52, 29, 53, 28, 31, 54,
49, 24, 27, 50, 26, 51, 48, 25, 29, 52, 55, 30, 54, 31, 28, 53,
28, 53, 54, 31, 55, 30, 29, 52, 48, 25, 26, 51, 27, 50, 49, 24
}, { // parities of third byte
63, 14, 13, 60, 12, 61, 62, 15, 11, 58, 57, 8, 56, 9, 10, 59,
10, 59, 56, 9, 57, 8, 11, 58, 62, 15, 12, 61, 13, 60, 63, 14,
9, 56, 59, 10, 58, 11, 8, 57, 61, 12, 15, 62, 14, 63, 60, 13,
60, 13, 14, 63, 15, 62, 61, 12, 8, 57, 58, 11, 59, 10, 9, 56,
8, 57, 58, 11, 59, 10, 9, 56, 60, 13, 14, 63, 15, 62, 61, 12,
61, 12, 15, 62, 14, 63, 60, 13, 9, 56, 59, 10, 58, 11, 8, 57,
62, 15, 12, 61, 13, 60, 63, 14, 10, 59, 56, 9, 57, 8, 11, 58,
11, 58, 57, 8, 56, 9, 10, 59, 63, 14, 13, 60, 12, 61, 62, 15,
31, 46, 45, 28, 44, 29, 30, 47, 43, 26, 25, 40, 24, 41, 42, 27,
42, 27, 24, 41, 25, 40, 43, 26, 30, 47, 44, 29, 45, 28, 31, 46,
41, 24, 27, 42, 26, 43, 40, 25, 29, 44, 47, 30, 46, 31, 28, 45,
28, 45, 46, 31, 47, 30, 29, 44, 40, 25, 26, 43, 27, 42, 41, 24,
40, 25, 26, 43, 27, 42, 41, 24, 28, 45, 46, 31, 47, 30, 29, 44,
29, 44, 47, 30, 46, 31, 28, 45, 41, 24, 27, 42, 26, 43, 40, 25,
30, 47, 44, 29, 45, 28, 31, 46, 42, 27, 24, 41, 25, 40, 43, 26,
43, 26, 25, 40, 24, 41, 42, 27, 31, 46, 45, 28, 44, 29, 30, 47
}
};
// table to extract the lower 4 bit from hamm24/18 encoded bytes
static char hamm24val[256] =
{
0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1,
2, 2, 2, 2, 3, 3, 3, 3, 2, 2, 2, 2, 3, 3, 3, 3,
4, 4, 4, 4, 5, 5, 5, 5, 4, 4, 4, 4, 5, 5, 5, 5,
6, 6, 6, 6, 7, 7, 7, 7, 6, 6, 6, 6, 7, 7, 7, 7,
8, 8, 8, 8, 9, 9, 9, 9, 8, 8, 8, 8, 9, 9, 9, 9,
10, 10, 10, 10, 11, 11, 11, 11, 10, 10, 10, 10, 11, 11, 11, 11,
12, 12, 12, 12, 13, 13, 13, 13, 12, 12, 12, 12, 13, 13, 13, 13,
14, 14, 14, 14, 15, 15, 15, 15, 14, 14, 14, 14, 15, 15, 15, 15,
0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1,
2, 2, 2, 2, 3, 3, 3, 3, 2, 2, 2, 2, 3, 3, 3, 3,
4, 4, 4, 4, 5, 5, 5, 5, 4, 4, 4, 4, 5, 5, 5, 5,
6, 6, 6, 6, 7, 7, 7, 7, 6, 6, 6, 6, 7, 7, 7, 7,
8, 8, 8, 8, 9, 9, 9, 9, 8, 8, 8, 8, 9, 9, 9, 9,
10, 10, 10, 10, 11, 11, 11, 11, 10, 10, 10, 10, 11, 11, 11, 11,
12, 12, 12, 12, 13, 13, 13, 13, 12, 12, 12, 12, 13, 13, 13, 13,
14, 14, 14, 14, 15, 15, 15, 15, 14, 14, 14, 14, 15, 15, 15, 15
};
// mapping from parity checks made by table hamm24par to error
// results return by hamm24.
// (0 = no error, 0x0100 = single bit error, 0x1000 = double error)
static short hamm24err[64] =
{
0x0000, 0x1000, 0x1000, 0x1000, 0x1000, 0x1000, 0x1000, 0x1000,
0x1000, 0x1000, 0x1000, 0x1000, 0x1000, 0x1000, 0x1000, 0x1000,
0x1000, 0x1000, 0x1000, 0x1000, 0x1000, 0x1000, 0x1000, 0x1000,
0x1000, 0x1000, 0x1000, 0x1000, 0x1000, 0x1000, 0x1000, 0x1000,
0x0100, 0x0100, 0x0100, 0x0100, 0x0100, 0x0100, 0x0100, 0x0100,
0x0100, 0x0100, 0x0100, 0x0100, 0x0100, 0x0100, 0x0100, 0x0100,
0x0100, 0x0100, 0x0100, 0x0100, 0x0100, 0x0100, 0x0100, 0x0100,
0x1000, 0x1000, 0x1000, 0x1000, 0x1000, 0x1000, 0x1000, 0x1000,
};
// mapping from parity checks made by table hamm24par to faulty bit
// in the decoded 18 bit word.
static int hamm24cor[64] =
{
0x00000, 0x00000, 0x00000, 0x00000, 0x00000, 0x00000, 0x00000, 0x00000,
0x00000, 0x00000, 0x00000, 0x00000, 0x00000, 0x00000, 0x00000, 0x00000,
0x00000, 0x00000, 0x00000, 0x00000, 0x00000, 0x00000, 0x00000, 0x00000,
0x00000, 0x00000, 0x00000, 0x00000, 0x00000, 0x00000, 0x00000, 0x00000,
0x00000, 0x00000, 0x00000, 0x00001, 0x00000, 0x00002, 0x00004, 0x00008,
0x00000, 0x00010, 0x00020, 0x00040, 0x00080, 0x00100, 0x00200, 0x00400,
0x00000, 0x00800, 0x01000, 0x02000, 0x04000, 0x08000, 0x10000, 0x20000,
0x00000, 0x00000, 0x00000, 0x00000, 0x00000, 0x00000, 0x00000, 0x00000,
};
int hamm8(u8 *p, int *err)
{
int a = hammtab[p[0]];
*err += a;
return a & 15;
}
int hamm16(u8 *p, int *err)
{
int a = hammtab[p[0]];
int b = hammtab[p[1]];
*err += a;
*err += b;
return (a & 15) | (b & 15) * 16;
}
int hamm24(u8 *p, int *err)
{
int e = hamm24par[0][p[0]] ^ hamm24par[1][p[1]] ^ hamm24par[2][p[2]];
int x = hamm24val[p[0]] + p[1] % 128 * 16 + p[2] % 128 * 2048;
*err += hamm24err[e];
return x ^ hamm24cor[e];
}
int chk_parity(u8 *p, int n)
{
int err;
for (err = 0; n--; p++)
if (hamm24par[0][*p] & 32)
*p &= 0x7f;
else
*p = BAD_CHAR, err++;
return err;
}
|
