+++ /dev/null
-/**
- *
- * This is a simple Reed-Solomon encoder
- * (C) Cliff Hones 2004
- *
- * This program 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 2 of the License, or
- * (at your option) any later version.
- *
- * This program 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 this program; if not, write to the Free Software
- * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
- *
- */
-
-// It is not written with high efficiency in mind, so is probably
-// not suitable for real-time encoding. The aim was to keep it
-// simple, general and clear.
-//
-// <Some notes on the theory and implementation need to be added here>
-
-// Usage:
-// First call rs_init_gf(poly) to set up the Galois Field parameters.
-// Then call rs_init_code(size, index) to set the encoding size
-// Then call rs_encode(datasize, data, out) to encode the data.
-//
-// These can be called repeatedly as required - but note that
-// rs_init_code must be called following any rs_init_gf call.
-//
-// If the parameters are fixed, some of the statics below can be
-// replaced with constants in the obvious way, and additionally
-// malloc/free can be avoided by using static arrays of a suitable
-// size.
-
-#include <stdio.h> // only needed for debug (main)
-#include <stdlib.h> // only needed for malloc/free
-
-static int gfpoly;
-static int symsize; // in bits
-static int logmod; // 2**symsize - 1
-static int rlen;
-
-static int *log = NULL, *alog = NULL, *rspoly = NULL;
-
-// rs_init_gf(poly) initialises the parameters for the Galois Field.
-// The symbol size is determined from the highest bit set in poly
-// This implementation will support sizes up to 30 bits (though that
-// will result in very large log/antilog tables) - bit sizes of
-// 8 or 4 are typical
-//
-// The poly is the bit pattern representing the GF characteristic
-// polynomial. e.g. for ECC200 (8-bit symbols) the polynomial is
-// a**8 + a**5 + a**3 + a**2 + 1, which translates to 0x12d.
-
-void rs_init_gf(int poly)
-{
- int m, b, p, v;
-
- // Return storage from previous setup
- if (log) {
- free(log);
- free(alog);
- free(rspoly);
- rspoly = NULL;
- }
- // Find the top bit, and hence the symbol size
- for (b = 1, m = 0; b <= poly; b <<= 1)
- m++;
- b >>= 1;
- m--;
- gfpoly = poly;
- symsize = m;
-
- // Calculate the log/alog tables
- logmod = (1 << m) - 1;
- log = (int *)malloc(sizeof(int) * (logmod + 1));
- alog = (int *)malloc(sizeof(int) * logmod);
-
- for (p = 1, v = 0; v < logmod; v++) {
- alog[v] = p;
- log[p] = v;
- p <<= 1;
- if (p & b)
- p ^= poly;
- }
-}
-
-// rs_init_code(nsym, index) initialises the Reed-Solomon encoder
-// nsym is the number of symbols to be generated (to be appended
-// to the input data). index is usually 1 - it is the index of
-// the constant in the first term (i) of the RS generator polynomial:
-// (x + 2**i)*(x + 2**(i+1))*... [nsym terms]
-// For ECC200, index is 1.
-
-void rs_init_code(int nsym, int index)
-{
- int i, k;
-
- if (rspoly)
- free(rspoly);
- rspoly = (int *)malloc(sizeof(int) * (nsym + 1));
-
- rlen = nsym;
-
- rspoly[0] = 1;
- for (i = 1; i <= nsym; i++) {
- rspoly[i] = 1;
- for (k = i - 1; k > 0; k--) {
- if (rspoly[k])
- rspoly[k] =
- alog[(log[rspoly[k]] + index) % logmod];
- rspoly[k] ^= rspoly[k - 1];
- }
- rspoly[0] = alog[(log[rspoly[0]] + index) % logmod];
- index++;
- }
-}
-
-// Note that the following uses byte arrays, so is only suitable for
-// symbol sizes up to 8 bits. Just change the data type of data and res
-// to unsigned int * for larger symbols.
-
-void rs_encode(int len, unsigned char *data, unsigned char *res)
-{
- int i, k, m;
- for (i = 0; i < rlen; i++)
- res[i] = 0;
- for (i = 0; i < len; i++) {
- m = res[rlen - 1] ^ data[i];
- for (k = rlen - 1; k > 0; k--) {
- if (m && rspoly[k])
- res[k] =
- res[k -
- 1] ^ alog[(log[m] +
- log[rspoly[k]]) % logmod];
- else
- res[k] = res[k - 1];
- }
- if (m && rspoly[0])
- res[0] = alog[(log[m] + log[rspoly[0]]) % logmod];
- else
- res[0] = 0;
- }
-}
-
-#ifndef LIB
-// The following tests the routines with the ISO/IEC 16022 Annexe R data
-int main(void)
-{
- register int i;
-
- unsigned char data[9] = { 142, 164, 186 };
- unsigned char out[5];
-
- rs_init_gf(0x12d);
- rs_init_code(5, 1);
-
- rs_encode(3, data, out);
-
- printf("Result of Annexe R encoding:\n");
- for (i = 4; i >= 0; i--)
- printf(" %d\n", out[i]);
-
- return 0;
-}
-#endif
projects / glabels / blobdiff