srsRAN_4G/lte/phy/lib/fec/src/turbocoder.c

/**
 *
 * \section COPYRIGHT
 *
 * Copyright 2013-2014 The libLTE Developers. See the
 * COPYRIGHT file at the top-level directory of this distribution.
 *
 * \section LICENSE
 *
 * This file is part of the libLTE library.
 *
 * libLTE 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 3 of
 * the License, or (at your option) any later version.
 *
 * libLTE 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.
 *
 * A copy of the GNU Lesser General Public License can be found in
 * the LICENSE file in the top-level directory of this distribution
 * and at http://www.gnu.org/licenses/.
 *
 */


#include "liblte/phy/fec/turbocoder.h"
#include <stdio.h>

#define NOF_REGS 3

int tcod_init(tcod_t *h, int max_long_cb) {

  if (tc_interl_init(&h->interl, max_long_cb)) {
    return -1;
  }
  h->max_long_cb = max_long_cb;
  return 0;
}

void tcod_free(tcod_t *h) {
  tc_interl_free(&h->interl);
  h->max_long_cb = 0;
}

int tcod_encode(tcod_t *h, char *input, char *output, int long_cb) {

  char reg1_0, reg1_1, reg1_2, reg2_0, reg2_1, reg2_2;
  int i, k = 0, j;
  char bit;
  char in, out;
  int *per;

  if (long_cb > h->max_long_cb) {
    fprintf(stderr, "Turbo coder initiated for max_long_cb=%d\n",
        h->max_long_cb);
    return -1;
  }

  if (tc_interl_LTE_gen(&h->interl, long_cb)) {
    fprintf(stderr, "Error initiating TC interleaver\n");
    return -1;
  }

  per = h->interl.forward;

  reg1_0 = 0;
  reg1_1 = 0;
  reg1_2 = 0;

  reg2_0 = 0;
  reg2_1 = 0;
  reg2_2 = 0;

  k = 0;
  for (i = 0; i < long_cb; i++) {
    bit = input[i];

    output[k] = bit;
    k++;

    in = bit ^ (reg1_2 ^ reg1_1);
    out = reg1_2 ^ (reg1_0 ^ in);

    reg1_2 = reg1_1;
    reg1_1 = reg1_0;
    reg1_0 = in;

    output[k] = out;
    k++;

    bit = input[per[i]];

    in = bit ^ (reg2_2 ^ reg2_1);
    out = reg2_2 ^ (reg2_0 ^ in);

    reg2_2 = reg2_1;
    reg2_1 = reg2_0;
    reg2_0 = in;

    output[k] = out;
    k++;
  }

  k = 3 * long_cb;

  /* TAILING CODER #1 */
  for (j = 0; j < NOF_REGS; j++) {
    bit = reg1_2 ^ reg1_1;

    output[k] = bit;
    k++;

    in = bit ^ (reg1_2 ^ reg1_1);
    out = reg1_2 ^ (reg1_0 ^ in);

    reg1_2 = reg1_1;
    reg1_1 = reg1_0;
    reg1_0 = in;

    output[k] = out;
    k++;
  }

  /* TAILING CODER #2 */
  for (j = 0; j < NOF_REGS; j++) {
    bit = reg2_2 ^ reg2_1;

    output[k] = bit;
    k++;

    in = bit ^ (reg2_2 ^ reg2_1);
    out = reg2_2 ^ (reg2_0 ^ in);

    reg2_2 = reg2_1;
    reg2_1 = reg2_0;
    reg2_0 = in;

    output[k] = out;
    k++;
  }
  return 0;
}