/* * Reed Solomon Encoder/Decoder * * 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 . * Commercial licensing is available under a separate license, please * contact author for details. * * Source code is available at http://rscode.sourceforge.net */ #define LOGEMERGENCY 0 #define LOGALERT 1 #define LOGCRIT 2 #define LOGERROR 3 #define LOGWARNING 4 #define LOGNOTICE 5 #define LOGINFO 6 #define LOGDEBUG 7 #include #include #include #include "ecc.h" void Debugprintf(const char * format, ...); /* Encoder parity bytes */ int pBytes[MAXDEG]; /* Decoder syndrome bytes */ int synBytes[MAXDEG]; /* generator polynomial */ int genPoly[MAXDEG*2]; int DEBUG = FALSE; //RUE; static void compute_genpoly (int nbytes, int genpoly[]); /* Initialize lookup tables, polynomials, etc. */ void initialize_ecc () { /* Initialize the galois field arithmetic tables */ init_galois_tables(); /* Compute the encoder generator polynomial */ compute_genpoly(NPAR, genPoly); } void zero_fill_from (unsigned char buf[], int from, int to) { int i; for (i = from; i < to; i++) buf[i] = 0; } /* debugging routines */ void print_parity (void) { int i; Debugprintf("Parity Bytes: "); for (i = 0; i < NPAR; i++) Debugprintf("[%d]:%x, ",i,pBytes[i]); Debugprintf("\n"); } void print_syndrome (void) { int i; Debugprintf("Syndrome Bytes: "); for (i = 0; i < NPAR; i++) Debugprintf("[%d]:%x, ",i,synBytes[i]); Debugprintf("\n"); } /********************************************************** * Reed Solomon Decoder * * Computes the syndrome of a codeword. Puts the results * into the synBytes[] array. */ void decode_data(unsigned char data[], int nbytes) { int i, j, sum; for (j = 0; j < NPAR; j++) { sum = 0; for (i = 0; i < nbytes; i++) { sum = data[i] ^ gmult(gexp[j+1], sum); } synBytes[j] = sum; // Debugprintf("%d %d %d\r\n", i, synBytes[i], index_of[s[i]]); } } /* Check if the syndrome is zero */ int check_syndrome (void) { int i, nz = 0; for (i =0 ; i < NPAR; i++) { if (synBytes[i] != 0) { nz = 1; break; } } return nz; } void debug_check_syndrome (void) { int i; for (i = 0; i < 3; i++) { Debugprintf(" inv log S[%d]/S[%d] = %d\n", i, i+1, glog[gmult(synBytes[i], ginv(synBytes[i+1]))]); } } /* Create a generator polynomial for an n byte RS code. * The coefficients are returned in the genPoly arg. * Make sure that the genPoly array which is passed in is * at least n+1 bytes long. */ static void compute_genpoly (int nbytes, int genpoly[]) { int i, tp[256], tp1[256]; /* multiply (x + a^n) for n = 1 to nbytes */ zero_poly(tp1); tp1[0] = 1; for (i = 1; i <= nbytes; i++) { zero_poly(tp); tp[0] = gexp[i]; /* set up x+a^n */ tp[1] = 1; mult_polys(genpoly, tp, tp1); copy_poly(tp1, genpoly); } } /* Simulate a LFSR with generator polynomial for n byte RS code. * Pass in a pointer to the data array, and amount of data. * * The parity bytes are deposited into pBytes[], and the whole message * and parity are copied to dest to make a codeword. * */ void encode_data (unsigned char msg[], int nbytes, unsigned char dst[]) { int i ,dbyte, j; unsigned char LFSR[MAXNPAR+1]; for(i=0; i < NPAR+1; i++) LFSR[i]=0; // for (i = 0; i < nbytes; i++) for (i = nbytes-1; i >= 0; i--) // Order reversed for compatibility wiyh Rick' Code { dbyte = msg[i] ^ LFSR[NPAR-1]; for (j = NPAR-1; j > 0; j--) { LFSR[j] = LFSR[j-1] ^ gmult(genPoly[j], dbyte); } LFSR[0] = gmult(genPoly[0], dbyte); } // return the parity bytes memcpy(dst, LFSR, NPAR); }