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//
// fec_example.c
//
// This example demonstrates the interface for forward error-
// correction (FEC) codes. A buffer of data bytes is encoded and
// corrupted with several errors. The decoder then attempts to
// recover the original data set. The user may select the FEC
// scheme from the command-line interface.
// SEE ALSO: crc_example.c
// checksum_example.c
// packetizer_example.c
//
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <getopt.h>
#include "liquid.h"
// print usage/help message
void usage()
{
printf("fec_example [options]\n");
printf(" u/h : print usage\n");
printf(" n : input data size (number of uncoded bytes)\n");
printf(" c : coding scheme, (h74 default):\n");
liquid_print_fec_schemes();
}
int main(int argc, char*argv[])
{
// options
unsigned int n = 4; // data length (bytes)
unsigned int nmax = 2048; // maximum data length
fec_scheme fs = LIQUID_FEC_HAMMING74; // error-correcting scheme
int dopt;
while((dopt = getopt(argc,argv,"uhn:c:")) != EOF){
switch (dopt) {
case 'h':
case 'u': usage(); return 0;
case 'n': n = atoi(optarg); break;
case 'c':
fs = liquid_getopt_str2fec(optarg);
if (fs == LIQUID_FEC_UNKNOWN) {
fprintf(stderr,"error: unknown/unsupported fec scheme \"%s\"\n\n",optarg);
exit(1);
}
break;
default:
exit(1);
}
}
// ensure proper data length
n = (n > nmax) ? nmax : n;
// create arrays
unsigned int n_enc = fec_get_enc_msg_length(fs,n);
printf("dec msg len : %u\n", n);
printf("enc msg len : %u\n", n_enc);
unsigned char data[n]; // original data message
unsigned char msg_enc[n_enc]; // encoded data message
unsigned char msg_cor[n_enc]; // corrupted data message
unsigned char msg_dec[n]; // decoded data message
// create object
fec q = fec_create(fs,NULL);
fec_print(q);
unsigned int i;
// create message
for (i=0; i<n; i++)
data[i] = rand() & 0xff;
// encode message
fec_encode(q, n, data, msg_enc);
// corrupt encoded message
memmove(msg_cor, msg_enc, n_enc);
msg_cor[0] ^= 0x04; // position 5
#if 0
msg_cor[1] ^= 0x04; //
msg_cor[2] ^= 0x02; //
msg_cor[3] ^= 0x01; //
msg_cor[4] ^= 0x80; //
msg_cor[5] ^= 0x40; //
msg_cor[6] ^= 0x20; //
msg_cor[7] ^= 0x10; //
#endif
// decode message
fec_decode(q, n, msg_cor, msg_dec);
printf("original message: [%3u] ",n);
for (i=0; i<n; i++)
printf(" %.2X", (unsigned int) (data[i]));
printf("\n");
printf("encoded message: [%3u] ",n_enc);
for (i=0; i<n_enc; i++)
printf(" %.2X", (unsigned int) (msg_enc[i]));
printf("\n");
printf("corrupted message: [%3u] ",n_enc);
for (i=0; i<n_enc; i++)
printf("%c%.2X", msg_cor[i]==msg_enc[i] ? ' ' : '*', (unsigned int) (msg_cor[i]));
printf("\n");
printf("decoded message: [%3u] ",n);
for (i=0; i<n; i++)
printf("%c%.2X", msg_dec[i] == data[i] ? ' ' : '*', (unsigned int) (msg_dec[i]));
printf("\n");
printf("\n");
// count bit errors
unsigned int j, num_sym_errors=0, num_bit_errors=0;
unsigned char e;
for (i=0; i<n; i++) {
num_sym_errors += (data[i] == msg_dec[i]) ? 0 : 1;
e = data[i] ^ msg_dec[i];
for (j=0; j<8; j++) {
num_bit_errors += e & 0x01;
e >>= 1;
}
}
//printf("number of symbol errors detected: %d\n", num_errors_detected);
printf("number of symbol errors received: %3u / %3u\n", num_sym_errors, n);
printf("number of bit errors received: %3u / %3u\n", num_bit_errors, n*8);
// clean up objects
fec_destroy(q);
return 0;
}
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