Error correction for network packets, proof of concept (untested)

Signed-off-by: Stephen L. <lrq3000@gmail.com>
2025-06-04 19:01:20 +00:00 · 2017-03-05 16:15:13 +01:00 · 2017-03-05 16:15:13 +01:00 · 7fa30ea26a
commit 7fa30ea26a
parent 0374f0710b
14 changed files with 1863 additions and 1 deletions
--- a/code/rscode/example.c
+++ b/code/rscode/example.c
@ -0,0 +1,128 @@
+/* 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 "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);
+}
+