LimeReport/3rdparty/zint-2.6.1/backend/reedsol.c

/** 
 
  This is a simple Reed-Solomon encoder
  (C) Cliff Hones 2004
 
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    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
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    IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
    ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
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    DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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 */

// 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
#include "reedsol.h"
static int logmod; // 2**symsize - 1
static int rlen;

static int *logt = 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(const int poly) {
    int m, b, p, v;

    // Find the top bit, and hence the symbol size
    for (b = 1, m = 0; b <= poly; b <<= 1)
        m++;
    b >>= 1;
    m--;

    // Calculate the log/alog tables
    logmod = (1 << m) - 1;
    logt = (int *) malloc(sizeof (int) * (logmod + 1));
    alog = (int *) malloc(sizeof (int) * logmod);

    for (p = 1, v = 0; v < logmod; v++) {
        alog[v] = p;
        logt[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(const int nsym, int index) {
    int i, k;

    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[(logt[rspoly[k]] + index) % logmod];
            rspoly[k] ^= rspoly[k - 1];
        }
        rspoly[0] = alog[(logt[rspoly[0]] + index) % logmod];
        index++;
    }
}

void rs_encode(const size_t len,const 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] = (unsigned char) (res[k - 1] ^ alog[(logt[m] + logt[rspoly[k]]) % logmod]);
            else
                res[k] = res[k - 1];
        }
        if (m && rspoly[0])
            res[0] = (unsigned char) (alog[(logt[m] + logt[rspoly[0]]) % logmod]);
        else
            res[0] = 0;
    }
}

/* The same as above but for larger bitlengths - Aztec code compatible */
void rs_encode_long(const int len, const unsigned int *data, unsigned int *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[(logt[m] + logt[rspoly[k]]) % logmod];
            else
                res[k] = res[k - 1];
        }
        if (m && rspoly[0])
            res[0] = alog[(logt[m] + logt[rspoly[0]]) % logmod];
        else
            res[0] = 0;
    }
}

/* Free memory */
void rs_free(void) {
    free(logt);
    free(alog);
    free(rspoly);
    rspoly = NULL;
}