/* 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[] = "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 */voidbyte_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.*/voidbyte_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;}voidmain (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);}