example.c

RS译码器的C源代码,采用了BM算法

/* Example use of Reed-Solomon library 
 *
 * (C) Universal Access Inc. 1996
 *
 * 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 "ecc.h"
 
//unsigned char msg[] ="000000000000000aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";//"Nervously I loaded the twin ducks aboard the revolving platform.";

//unsigned char msg[] ="000000000000000aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";//"Nervously I loaded the twin ducks aboard the revolving platform.";
unsigned char msg[] ="000000000000000aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";//"Nervously I loaded the twin ducks aboard the revolving platform.";

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;
}


void
main (int argc, char *argv[])
{
 
  int erasures[32];
  int nerasures = 0;
  //int i;

  /* 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);
    for(i=0;i<256;i++)
	  printf("Encoded data is: %d\n", codeword[i]);
 */
#define ML (sizeof (msg) + NPAR)




  byte_err(0x35, 16, codeword);
  byte_err(0x35, 17, codeword);
  byte_err(0x23, 18, codeword);
  byte_err(0x34, 19, codeword);
  byte_err(0x35, 20, codeword);
  byte_err(0x23, 21, codeword);
  byte_err(0x34, 22, codeword);
  byte_err(0x35, 23, codeword);
  byte_err(0x35, 50, codeword);
  byte_err(0x35, 51, codeword);
  byte_err(0x23, 52, codeword);
  byte_err(0x34, 53, codeword);
  byte_err(0x35, 54, codeword);
  byte_err(0x23, 55, codeword);
  byte_err(0x34, 56, codeword);
  byte_err(0x35, 57, codeword);
  byte_err(0x35, 90, codeword);
  byte_err(0x23, 91, codeword);
  byte_err(0x34, 92, codeword);
  byte_err(0x35, 93, codeword);
  byte_err(0x23, 94, codeword);
  byte_err(0x34, 95, codeword);
  byte_err(0x23, 96, codeword);
  byte_err(0x23, 120, codeword);

  byte_err(0x34, 150, codeword);
  byte_err(0x35, 151, codeword);
  byte_err(0x23, 152, codeword);
  byte_err(0x34, 180, codeword);
  byte_err(0x34, 181, codeword);
  byte_err(0x34, 188, codeword);
  byte_err(0x35, 189, codeword);
  byte_err(0x35, 190, codeword);
  byte_err(0x35, 191, 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... */

 /* for(i=0;i<256;i++)
	  printf("Encoded data is: %d\n", codeword[i]);
 
  /* 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);
}