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129 lines
3.4 KiB
C
129 lines
3.4 KiB
C
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/* Example use of Reed-Solomon library
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*
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* Copyright Henry Minsky (hqm@alum.mit.edu) 1991-2009
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*
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* This software library is licensed under terms of the GNU GENERAL
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* PUBLIC LICENSE
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*
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* RSCODE is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* RSCODE is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with Rscode. If not, see <http://www.gnu.org/licenses/>.
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* Commercial licensing is available under a separate license, please
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* contact author for details.
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*
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* This same code demonstrates the use of the encodier and
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* decoder/error-correction routines.
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*
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* We are assuming we have at least four bytes of parity (NPAR >= 4).
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*
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* This gives us the ability to correct up to two errors, or
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* four erasures.
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*
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* In general, with E errors, and K erasures, you will need
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* 2E + K bytes of parity to be able to correct the codeword
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* back to recover the original message data.
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*
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* You could say that each error 'consumes' two bytes of the parity,
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* whereas each erasure 'consumes' one byte.
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*
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* Thus, as demonstrated below, we can inject one error (location unknown)
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* and two erasures (with their locations specified) and the
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* error-correction routine will be able to correct the codeword
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* back to the original message.
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* */
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#include <stdio.h>
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#include <stdlib.h>
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#include "ecc.h"
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unsigned char msg[] = "Nervously I loaded the twin ducks aboard the revolving pl\
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atform.";
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unsigned char codeword[256];
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/* Some debugging routines to introduce errors or erasures
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into a codeword.
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*/
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/* Introduce a byte error at LOC */
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void
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byte_err (int err, int loc, unsigned char *dst)
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{
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printf("Adding Error at loc %d, data %#x\n", loc, dst[loc-1]);
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dst[loc-1] ^= err;
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}
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/* Pass in location of error (first byte position is
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labeled starting at 1, not 0), and the codeword.
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*/
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void
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byte_erasure (int loc, unsigned char dst[], int cwsize, int erasures[])
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{
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printf("Erasure at loc %d, data %#x\n", loc, dst[loc-1]);
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dst[loc-1] = 0;
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}
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int
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main (int argc, char *argv[])
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{
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int erasures[16];
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int nerasures = 0;
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/* Initialization the ECC library */
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initialize_ecc ();
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/* ************** */
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/* Encode data into codeword, adding NPAR parity bytes */
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encode_data(msg, sizeof(msg), codeword);
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printf("Encoded data is: \"%s\"\n", codeword);
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#define ML (sizeof (msg) + NPAR)
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/* Add one error and two erasures */
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byte_err(0x35, 3, codeword);
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byte_err(0x23, 17, codeword);
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byte_err(0x34, 19, codeword);
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printf("with some errors: \"%s\"\n", codeword);
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/* We need to indicate the position of the erasures. Eraseure
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positions are indexed (1 based) from the end of the message... */
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erasures[nerasures++] = ML-17;
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erasures[nerasures++] = ML-19;
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/* Now decode -- encoded codeword size must be passed */
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decode_data(codeword, ML);
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/* check if syndrome is all zeros */
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if (check_syndrome () != 0) {
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correct_errors_erasures (codeword,
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ML,
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nerasures,
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erasures);
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printf("Corrected codeword: \"%s\"\n", codeword);
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}
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exit(0);
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}
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