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/*
* 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>
void
ao_fec_dump_bytes(uint8_t *bytes, uint16_t len, 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");
}
static uint16_t inline
crc_byte(uint8_t byte, uint16_t crc)
{
uint8_t bit;
for (bit = 0; bit < 8; bit++) {
if (((crc & 0x8000) >> 8) ^ (byte & 0x80))
crc = (crc << 1) ^ 0x8005;
else
crc = (crc << 1);
byte <<= 1;
}
return crc;
}
uint16_t
ao_fec_crc(uint8_t *bytes, uint8_t len)
{
uint16_t crc = AO_FEC_CRC_INIT;
while (len--)
crc = 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(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;
}
uint8_t
ao_fec_prepare(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"
};
#if 0
void
ao_fec_whiten(uint8_t *in, uint8_t len, uint8_t *out)
{
const uint8_t *w = ao_fec_whiten_table;
while (len--)
*out++ = *in++ ^ *w++;
}
/*
* Unused as interleaving is now built in to ao_fec_encode
*/
static void
ao_fec_interleave(uint8_t *d, uint8_t len)
{
uint8_t i, j;
for (i = 0; i < len; i += 4) {
uint32_t interleaved = 0;
for (j = 0; j < 4 * 4; j++) {
interleaved <<= 2;
interleaved |= (d[i + (~j & 0x3)] >> (2 * ((j & 0xc) >> 2))) & 0x03;
}
d[i+0] = interleaved >> 24;
d[i+1] = interleaved >> 16;
d[i+2] = interleaved >> 8;
d[i+3] = interleaved;
}
}
#endif
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(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;
}
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