--- /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