/*
* qrencode - QR Code encoder
*
* Reed solomon error correction code encoder specialized for QR code.
*
* Copyright (C) 2013 Kentaro Fukuchi <kentaro@fukuchi.org>
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or any later version.
*
* This library 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
#if HAVE_CONFIG_H
# include "config.h"
#endif
#include <stdlib.h>
#include <string.h>
#include "rsecc.h"
static int initialized = 0;
#define SYMBOL_SIZE (8)
#define symbols ((1 << SYMBOL_SIZE) - 1)
static const int proot = 0x11d; /* stands for x^8+x^4+x^3+x^2+1 (see pp.37 of JIS X0510:2004) */
/* min/max codeword length of ECC, calculated from the specification. */
#define min_length (2)
#define max_length (30)
#define max_generatorSize (max_length)
static unsigned char alpha[symbols + 1];
static unsigned char aindex[symbols + 1];
static unsigned char generator[max_length - min_length + 1][max_generatorSize + 1];
static unsigned char generatorInitialized[max_length - min_length + 1];
static void RSECC_initLookupTable(void)
{
int i, b;
alpha[symbols] = 0;
aindex[0] = symbols;
b = 1;
for(i = 0; i < symbols; i++) {
alpha[i] = b;
aindex[b] = i;
b <<= 1;
if(b & (symbols + 1)) {
b ^= proot;
}
b &= symbols;
}
}
void RSECC_init(void)
{
RSECC_initLookupTable();
memset(generatorInitialized, 0, (max_length - min_length + 1));
initialized = 1;
}
static void generator_init(int length)
{
int i, j, a;
int g[max_generatorSize + 1];
g[0] = 1;
a = 0;
for(i = 1; i <= length; i++) {
g[i] = 1;
for(j = i - 1; j > 0; j--) {
if(g[0] != 0) {
g[j] = g[j - 1] ^ alpha[(aindex[g[j]] + a) % symbols];
} else {
g[j] = g[j - 1];
}
}
g[0] = alpha[(aindex[g[0]] + a) % symbols];
a++;
}
for(i = 0; i <= length; i++) {
generator[length - min_length][i] = aindex[g[i]];
}
generatorInitialized[length - min_length] = 1;
}
int RSECC_encode(int datalength, int ecclength, const unsigned char *data, unsigned char *ecc)
{
int i, j;
unsigned char feedback;
unsigned char *gen;
if(!initialized) {
RSECC_init();
}
if(ecclength > max_length) return -1;
memset(ecc, 0, ecclength);
if(!generatorInitialized[ecclength - min_length]) generator_init(ecclength);
gen = generator[ecclength - min_length];
for(i = 0; i < datalength; i++) {
feedback = aindex[data[i] ^ ecc[0]];
if(feedback != symbols) {
for(j = 1; j < ecclength; j++) {
ecc[j] ^= alpha[(feedback + gen[ecclength - j]) % symbols];
}
}
memmove(&ecc[0], &ecc[1], ecclength - 1);
if(feedback != symbols) {
ecc[ecclength - 1] = alpha[(feedback + gen[0]) % symbols];
} else {
ecc[ecclength - 1] = 0;
}
}
return 0;
}
