content: /*******************************************************************************
   * Copyright 2014 Trevor Robinson
   * 
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   * 
   *   http://www.apache.org/licenses/LICENSE-2.0
   * 
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   ******************************************************************************/
  package com.scurrilous.circe.crc;
  
  /**
   * Implements a "normal" MSB-first long-width CRC function using a lookup table.
   * Does not support bit-widths less than 8.
   */
  final class NormalLongCrc extends AbstractLongCrc {
  
      private final long widthMask;
      private final long[] table = new long[256];
  
      NormalLongCrc(String algorithm, int bitWidth, long poly, long init, long xorOut) {
          super(algorithm, bitWidth, init, xorOut);
          if (bitWidth < 8)
              throw new IllegalArgumentException("invalid CRC width");
  
          widthMask = bitWidth < 64 ? ((1L << bitWidth) - 1) : ~0L;
          final long top = 1L << (bitWidth - 1);
          for (int i = 0; i < 256; ++i) {
              long crc = (long) i << (bitWidth - 8);
              for (int j = 0; j < 8; ++j)
                  crc = (crc & top) != 0 ? (crc << 1) ^ poly : crc << 1;
              table[i] = crc & widthMask;
          }
      }
  
      @Override
      protected long resumeRaw(long crc, byte[] input, int index, int length) {
          for (int i = 0; i < length; ++i)
              crc = table[(int) ((crc >>> (bitWidth - 8)) ^ input[index + i]) & 0xff] ^ (crc << 8);
          return crc & widthMask;
      }
  }
  