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
|
/*
* Copyright © 2012 Keith Packard <keithp@keithp.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; version 2 of the License.
*
* 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 General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
*/
#include <ao_fec.h>
#include <stdio.h>
#if AO_FEC_DEBUG
void
ao_fec_dump_bytes(const uint8_t *bytes, uint16_t len, const char *name)
{
uint16_t i;
printf ("%s (%d):", name, len);
for (i = 0; i < len; i++) {
if ((i & 7) == 0)
printf ("\n\t%02x:", i);
printf(" %02x", bytes[i]);
}
printf ("\n");
}
#endif
uint16_t
ao_fec_crc(const uint8_t *bytes, uint8_t len)
{
uint16_t crc = AO_FEC_CRC_INIT;
while (len--)
crc = ao_fec_crc_byte(*bytes++, crc);
return crc;
}
/*
* len is the length of the data; the crc will be
* the fist two bytes after that
*/
uint8_t
ao_fec_check_crc(const uint8_t *bytes, uint8_t len)
{
uint16_t computed_crc = ao_fec_crc(bytes, len);
uint16_t received_crc = (bytes[len] << 8) | (bytes[len+1]);
return computed_crc == received_crc;
}
/*
* Compute CRC and trellis-terminator/interleave-pad bytes
*/
static uint8_t
ao_fec_prepare(const uint8_t *in, uint8_t len, uint8_t *extra)
{
uint16_t crc = ao_fec_crc (in, len);
uint8_t i = 0;
uint8_t num_fec;
/* Append CRC */
extra[i++] = crc >> 8;
extra[i++] = crc;
/* Append FEC -- 1 byte if odd, two bytes if even */
num_fec = 2 - (i & 1);
while (num_fec--)
extra[i++] = AO_FEC_TRELLIS_TERMINATOR;
return i;
}
const uint8_t ao_fec_whiten_table[] = {
#include "ao_whiten.h"
};
static const uint8_t ao_fec_encode_table[16] = {
/* next 0 1 state */
0, 3, /* 000 */
1, 2, /* 001 */
3, 0, /* 010 */
2, 1, /* 011 */
3, 0, /* 100 */
2, 1, /* 101 */
0, 3, /* 110 */
1, 2 /* 111 */
};
uint8_t
ao_fec_encode(const uint8_t *in, uint8_t len, uint8_t *out)
{
uint8_t extra[AO_FEC_PREPARE_EXTRA];
uint8_t extra_len;
uint32_t encode, interleave;
uint8_t pair, byte, bit;
uint16_t fec = 0;
const uint8_t *whiten = ao_fec_whiten_table;
extra_len = ao_fec_prepare(in, len, extra);
for (pair = 0; pair < len + extra_len; pair += 2) {
encode = 0;
for (byte = 0; byte < 2; byte++) {
if (pair + byte == len)
in = extra;
fec |= *in++ ^ *whiten++;
for (bit = 0; bit < 8; bit++) {
encode = encode << 2 | ao_fec_encode_table[fec >> 7];
fec = (fec << 1) & 0x7ff;
}
}
interleave = 0;
for (bit = 0; bit < 4 * 4; bit++) {
uint8_t byte_shift = (bit & 0x3) << 3;
uint8_t bit_shift = (bit & 0xc) >> 1;
interleave = (interleave << 2) | ((encode >> (byte_shift + bit_shift)) & 0x3);
}
*out++ = interleave >> 24;
*out++ = interleave >> 16;
*out++ = interleave >> 8;
*out++ = interleave >> 0;
}
return (len + extra_len) * 2;
}
|
