text: /*
   * Copyright (c) 2006, Swedish Institute of Computer Science
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   * 3. Neither the name of the Institute nor the names of its contributors
   *    may be used to endorse or promote products derived from this software
   *    without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
   * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   * SUCH DAMAGE.
   *
   * This file is part of the Contiki operating system.
   *
   * @(#)$Id: gcr.c,v 1.2 2011/01/07 11:55:36 nifi Exp $
   */
  
  /**
   * \file
   *         Implementation of GCR coding/decoding
   * \author
   *         Joakim Eriksson <joakime@sics.se>
   *
   */
  
  /* GCR conversion table - used for converting ordinary byte to 10-bits */
  /* (or 4 bits to 5) */
  static const unsigned char GCR_encode[16] = {
      0x0a, 0x0b, 0x12, 0x13,
      0x0e, 0x0f, 0x16, 0x17,
      0x09, 0x19, 0x1a, 0x1b,
      0x0d, 0x1d, 0x1e, 0x15
  };
  
  /*  5 bits > 4 bits (0xff => invalid) */
  static const unsigned char GCR_decode[32] = {
      0xff, 0xff, 0xff, 0xff, // 0 - 3invalid...
      0xff, 0xff, 0xff, 0xff, // 4 - 7 invalid...
      0xff, 0x08, 0x00, 0x01, // 8 invalid... 9 = 8, a = 0, b = 1
      0xff, 0x0c, 0x04, 0x05, // c invalid... d = c, e = 4, f = 5
  
      0xff, 0xff, 0x02, 0x03, // 10-11 invalid...
      0xff, 0x0f, 0x06, 0x07, // 14 invalid...
      0xff, 0x09, 0x0a, 0x0b, // 18 invalid...
      0xff, 0x0d, 0x0e, 0xff, // 1c, 1f invalid...
    };
  
  static unsigned char gcr_bits = 0;
  static unsigned short gcr_val = 0;
  
  /* Call before starting encoding or decoding */
  void gcr_init() {
    gcr_val = 0;
    gcr_bits = 0;
  }
  
  /* Use this to check if encoding / decoding is complete for now */
  unsigned char gcr_finished() {
    return gcr_bits == 0;
  }
  
  /* Encode one character - and store in bits - get encoded with get_encoded */
  void gcr_encode(unsigned char raw_data) {
    gcr_val |=
      ((GCR_encode[raw_data >> 4u] << 5u ) |
       GCR_encode[raw_data & 0xf]) << gcr_bits;
    gcr_bits += 10;
  }
  
  /* Gets the current char of the encoded stream */
  unsigned char gcr_get_encoded(unsigned char *raw_data) {
    if (gcr_bits >= 8) {
      *raw_data = (unsigned char) (gcr_val & 0xff);
      gcr_val = gcr_val >> 8u;
      gcr_bits = gcr_bits - 8;
      return 1;
    }
    return 0;
  }
  
  /* Decode one char - result can be get from get_decoded */
  void gcr_decode(unsigned char gcr_data) {
    gcr_val |= gcr_data << gcr_bits;
    gcr_bits += 8;
  }
  
  /* check if the current decoded stream is correct */
  unsigned char gcr_valid() {
    if (gcr_bits >= 10) {
      unsigned short val = gcr_val & 0x3ff;
      if ((GCR_decode[val >> 5u] << 4u) == 0xff ||
  	(GCR_decode[val & 0x1f]) == 0xff) {
        return 0;
      }
    }
    return 1;
  }
  
  /* gets the decoded stream - if any char is available */
  unsigned char gcr_get_decoded(unsigned char *raw_data) {
    if (gcr_bits >= 10) {
      unsigned short val = gcr_val & 0x3ff;
      *raw_data = (unsigned char) ((GCR_decode[val >> 5] << 4) |
  				 (GCR_decode[val & 0x1f]));
      gcr_val = gcr_val >> 10;
      gcr_bits = gcr_bits - 10;
      return 1;
    }
    return 0;
  }
  
  /*
  static const char encoded[] = {
    0x4a, 0x25, 0xa5, 0xfc, 0x96, 0xff, 0xff, 0xb5, 0xd4, 0x5a, 0xea, 0xff, 0xff, 0xaa, 0xd3, 0xff
  };
  
  int main(int argc, char **argv) {
    // unsigned char c[] = "testing gcr 1 2 3 4 5 6...";
    unsigned char c[] = { 0, 8, 0xe0, 0x2b, 0xac, 0x10, 0x01, 0x11, 0x50, 0xff, 0xf4, 0xa4, 0x00 };
    unsigned char c2[200];
    int pos = 0, pos2 = 0, i = 0;
  
    printf("Testing GCR on: %s \n", c);
  
    gcr_init();
    for (i = 0; i < sizeof(c); i++) {
      gcr_encode(c[i]);
      while(gcr_get_encoded(&c2[pos])) {
        printf("%02x=>%02x ", c[i], c2[pos]);
        pos++;
      }
    }
    printf("\n");
    printf("Encoded result %d chars (from %d) \n", pos, i);
    gcr_init();
    for (i = 0; i < pos; i++) {
      gcr_decode(c2[i]);
      if(!gcr_valid()) {
        printf("GCR: not valid\n");
      }
      while(gcr_get_decoded(&c[pos2])) {
        pos2++;
      }
    }
    printf("GCR: %s\n",c);
  }
  */
  