2 * Copyright © 2012 Keith Packard <keithp@keithp.com>
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; version 2 of the License.
8 * This program is distributed in the hope that it will be useful, but
9 * WITHOUT ANY WARRANTY; without even the implied warranty of
10 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
11 * General Public License for more details.
13 * You should have received a copy of the GNU General Public License along
14 * with this program; if not, write to the Free Software Foundation, Inc.,
15 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
22 * 'input' is 8-bits per symbol soft decision data
23 * 'len' is output byte length
26 static const uint8_t ao_fec_encode_table[16] = {
43 ao_soft_sym(uint8_t bits)
47 s.a = ((bits & 2) >> 1) * 0xff;
48 s.b = (bits & 1) * 0xff;
53 ao_next_state(uint8_t state, uint8_t bit)
55 return ((state << 1) | bit) & 0x7;
58 static inline abs(int x) { return x < 0 ? -x : x; }
61 ao_cost(struct ao_soft_sym a, struct ao_soft_sym b)
63 return abs(a.a - b.a) + abs(a.b - b.b);
67 ao_fec_decode(uint8_t *in, int len, uint8_t *out)
69 int cost[len/2 + 1][8];
70 uint8_t prev[len/2 + 1][8];
73 uint8_t state = 0, min_state;
76 for (c = 0; c < 8; c++)
80 for (i = 0; i < len; i += 2) {
82 struct ao_soft_sym s = { .a = in[i], .b = in[i+1] };
84 for (state = 0; state < 8; state++)
85 cost[b+1][state] = 10000;
87 for (state = 0; state < 8; state++) {
88 struct ao_soft_sym zero = ao_soft_sym(ao_fec_encode_table[state * 2 + 0]);
89 struct ao_soft_sym one = ao_soft_sym(ao_fec_encode_table[state * 2 + 1]);
90 uint8_t zero_state = ao_next_state(state, 0);
91 uint8_t one_state = ao_next_state(state, 1);
92 int zero_cost = ao_cost(s, zero);
93 int one_cost = ao_cost(s, one);
96 printf ("saw %02x %02x expected %02x %02x (%d) or %02x %02x (%d)\n",
97 s.a, s.b, zero.a, zero.b, zero_cost, one.a, one.b, one_cost);
99 zero_cost += cost[b][state];
100 one_cost += cost[b][state];
101 if (zero_cost < cost[b+1][zero_state]) {
102 prev[b+1][zero_state] = state;
103 cost[b+1][zero_state] = zero_cost;
106 if (one_cost < cost[b+1][one_state]) {
107 prev[b+1][one_state] = state;
108 cost[b+1][one_state] = one_cost;
112 printf ("bit %3d symbol %2x %2x:", i/2, s.a, s.b);
113 for (state = 0; state < 8; state++) {
114 printf (" %5d", cost[b+1][state]);
122 for (state = 1; state < 8; state++) {
123 if (cost[b][state] < c) {
129 for (b = len/2; b > 0; b--) {
130 bits[b-1] = min_state & 1;
131 min_state = prev[b][min_state];
134 for (i = 0; i < len/2; i += 8) {
138 for (b = 0; b < 8; b++)
139 byte = (byte << 1) | bits[i + b];