#include <ao_fec.h>
#include <stdio.h>
+#if AO_FEC_DEBUG
void
-ao_fec_dump_bytes(uint8_t *bytes, uint8_t len, char *name)
+ao_fec_dump_bytes(const uint8_t *bytes, uint16_t len, const char *name)
{
- uint8_t i;
+ uint16_t i;
printf ("%s (%d):", name, len);
for (i = 0; i < len; 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;
-}
+#endif
uint16_t
-ao_fec_crc(uint8_t *bytes, uint8_t len)
+ao_fec_crc(const uint8_t *bytes, uint8_t len)
{
uint16_t crc = AO_FEC_CRC_INIT;
while (len--)
- crc = crc_byte(*bytes++, crc);
+ 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_prepare(uint8_t *in, uint8_t len, uint8_t *out)
+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;
+ uint8_t i = 0;
uint8_t num_fec;
- /* Copy data */
- for (i = 0; i < len; i++)
- out[i] = in[i];
-
/* Append CRC */
- out[i++] = crc >> 8;
- out[i++] = 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--)
- out[i++] = AO_FEC_TRELLIS_TERMINATOR;
+ extra[i++] = AO_FEC_TRELLIS_TERMINATOR;
return i;
}
-static const uint8_t whiten[] = {
+const uint8_t ao_fec_whiten_table[] = {
#include "ao_whiten.h"
};
-void
-ao_fec_whiten(uint8_t *in, uint8_t len, uint8_t *out)
-{
- const uint8_t *w = whiten;
-
- while (len--)
- *out++ = *in++ ^ *w++;
-}
-
static const uint8_t ao_fec_encode_table[16] = {
/* next 0 1 state */
0, 3, /* 000 */
};
uint8_t
-ao_fec_encode(uint8_t *in, uint8_t len, uint8_t *out)
+ao_fec_encode(const uint8_t *in, uint8_t len, uint8_t *out)
{
- uint16_t fec = 0, output;
- uint8_t byte, bit;
-
- for (byte = 0; byte < len; byte++) {
- fec = (fec & 0x700) | in[byte];
- output = 0;
- for (bit = 0; bit < 8; bit++) {
- output = output << 2 | ao_fec_encode_table[fec >> 7];
- fec = (fec << 1) & 0x7ff;
+ 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;
+ }
}
- out[byte * 2] = output >> 8;
- out[byte * 2 + 1] = output;
- }
- return len * 2;
-}
-
-uint8_t
-ao_fec_interleave(uint8_t *in, uint8_t len, uint8_t *out)
-{
- uint8_t i, j;
- for (i = 0; i < len; i += 4) {
- uint32_t interleaved = 0;
+ interleave = 0;
+ for (bit = 0; bit < 4 * 4; bit++) {
+ uint8_t byte_shift = (bit & 0x3) << 3;
+ uint8_t bit_shift = (bit & 0xc) >> 1;
- for (j = 0; j < 4 * 4; j++) {
- interleaved <<= 2;
- interleaved |= (in[i + (~j & 0x3)] >> (2 * ((j & 0xc) >> 2))) & 0x03;
+ interleave = (interleave << 2) | ((encode >> (byte_shift + bit_shift)) & 0x3);
}
- out[i+0] = interleaved >> 24;
- out[i+1] = interleaved >> 16;
- out[i+2] = interleaved >> 8;
- out[i+3] = interleaved;
+ *out++ = interleave >> 24;
+ *out++ = interleave >> 16;
+ *out++ = interleave >> 8;
+ *out++ = interleave >> 0;
}
- return len;
+ return (len + extra_len) * 2;
}