#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "../qrspec.h"
#include "rsecc_decoder.h"

#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];

void RSECC_decoder_init() {
    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;
    }
}

int RSECC_decoder_checkSyndrome(int dl, unsigned char *data, int el, unsigned char *ecc) {
    int i, j;
    int s;

    for (i = 0; i < el; i++) {
        s = data[0];
        for (j = 1; j < dl; j++) {
            if (s == 0) {
                s = data[j];
            } else {
                s = data[j] ^ alpha[(aindex[s] + i) % symbols];
            }
        }
        for (j = 0; j < el; j++) {
            if (s == 0) {
                s = ecc[j];
            } else {
                s = ecc[j] ^ alpha[(aindex[s] + i) % symbols];
            }
        }
        if (s != 0) {
            return -1;
        }
    }

    return 0;
}
