text: /**
   * Flake: FLAC audio encoder
   * Copyright (c) 2006  Justin Ruggles
   *
   * 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 of the License, or (at your option) 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 Street, Fifth Floor, Boston, MA 02110-1301 USA
   */
  
  #include "common.h"
  
  #include "crc.h"
  
  static void
  crc_init_table(uint16_t *table, int bits, int poly)
  {
      int i, j, crc;
  
      poly = (poly + (1<<bits));
      for(i=0; i<256; i++) {
          crc = i;
          for(j=0; j<bits; j++) {
              if(crc & (1<<(bits-1))) {
                  crc = (crc << 1) ^ poly;
              } else {
                  crc <<= 1;
              }
          }
          table[i] = (crc & ((1<<bits)-1));
      }
  }
  
  /* CRC key for polynomial, x^8 + x^2 + x^1 + 1 */
  #define CRC8_POLY 0x07
  
  /* CRC key for polynomial, x^16 + x^15 + x^2 + 1 */
  #define CRC16_POLY 0x8005
  
  static uint16_t crc8tab[256];
  static uint16_t crc16tab[256];
  
  void
  crc_init()
  {
      crc_init_table(crc8tab, 8, CRC8_POLY);
      crc_init_table(crc16tab, 16, CRC16_POLY);
  }
  
  static uint16_t
  calc_crc(const uint16_t *table, int bits, const uint8_t *data, uint32_t len)
  {
  	uint16_t crc, v1, v2;
  
      crc = 0;
      while(len--) {
          v1 = (crc << 8) & ((1 << bits) - 1);
          v2 = (crc >> (bits - 8)) ^ *data++;
          assert(v2 < 256);
          crc = v1 ^ table[v2];
      }
      return crc;
  }
  
  uint8_t
  calc_crc8(const uint8_t *data, uint32_t len)
  {
  	uint8_t crc;
  
      if(data == NULL) return 0;
  
      crc = calc_crc(crc8tab, 8, data, len);
      return crc;
  }
  
  uint16_t
  calc_crc16(const uint8_t *data, uint32_t len)
  {
  	uint16_t crc;
  
      if(data == NULL) return 0;
  
      crc = calc_crc(crc16tab, 16, data, len);
      return crc;
  }
  