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/* Example use of Reed-Solomon library
*
* Copyright Henry Minsky (hqm@alum.mit.edu) 1991-2009
*
* This software library is licensed under terms of the GNU GENERAL
* PUBLIC LICENSE
*
* RSCODE 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, either version 3 of the License, or
* (at your option) any later version.
*
* RSCODE 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 Rscode. If not, see <http://www.gnu.org/licenses/>.
* Commercial licensing is available under a separate license, please
* contact author for details.
*
* This same code demonstrates the use of the encodier and
* decoder/error-correction routines.
*
* We are assuming we have at least four bytes of parity (NPAR >= 4).
*
* This gives us the ability to correct up to two errors, or
* four erasures.
*
* In general, with E errors, and K erasures, you will need
* 2E + K bytes of parity to be able to correct the codeword
* back to recover the original message data.
*
* You could say that each error 'consumes' two bytes of the parity,
* whereas each erasure 'consumes' one byte.
*
* Thus, as demonstrated below, we can inject one error (location unknown)
* and two erasures (with their locations specified) and the
* error-correction routine will be able to correct the codeword
* back to the original message.
* */
#include <stdio.h>
#include <stdlib.h>
#include <rscode/ecc.h>
unsigned char msg[] = "Nervously I loaded the twin ducks aboard the revolving pl\
atform.";
unsigned char codeword[256];
/* Some debugging routines to introduce errors or erasures
into a codeword.
*/
/* Introduce a byte error at LOC */
void
byte_err (int err, int loc, unsigned char *dst)
{
printf("Adding Error at loc %d, data %#x\n", loc, dst[loc-1]);
dst[loc-1] ^= err;
}
/* Pass in location of error (first byte position is
labeled starting at 1, not 0), and the codeword.
*/
void
byte_erasure (int loc, unsigned char dst[], int cwsize, int erasures[])
{
printf("Erasure at loc %d, data %#x\n", loc, dst[loc-1]);
dst[loc-1] = 0;
}
int
main (int argc, char *argv[])
{
int erasures[16];
int nerasures = 0;
/* Initialization the ECC library */
initialize_ecc ();
/* ************** */
/* Encode data into codeword, adding NPAR parity bytes */
encode_data(msg, sizeof(msg), codeword);
printf("Encoded data is: \"%s\"\n", codeword);
#define ML (sizeof (msg) + NPAR)
/* Add one error and two erasures */
byte_err(0x35, 3, codeword);
byte_err(0x23, 17, codeword);
byte_err(0x34, 19, codeword);
printf("with some errors: \"%s\"\n", codeword);
/* We need to indicate the position of the erasures. Eraseure
positions are indexed (1 based) from the end of the message... */
erasures[nerasures++] = ML-17;
erasures[nerasures++] = ML-19;
/* Now decode -- encoded codeword size must be passed */
decode_data(codeword, ML);
/* check if syndrome is all zeros */
if (check_syndrome () != 0) {
correct_errors_erasures (codeword,
ML,
nerasures,
erasures);
printf("Corrected codeword: \"%s\"\n", codeword);
}
exit(0);
}
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