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 byte-width CRC function using a lookup table.
   */
  final class NormalByteCrc extends AbstractIntCrc {
  
      private final byte[] table = new byte[256];
  
      NormalByteCrc(String algorithm, int bitWidth, int poly, int init, int xorOut) {
          super(algorithm, bitWidth, init, xorOut);
          if (bitWidth > 8)
              throw new IllegalArgumentException("invalid CRC width");
  
          final int widthMask = (1 << bitWidth) - 1;
          final int shpoly = poly << (8 - bitWidth);
          for (int i = 0; i < 256; ++i) {
              int crc = i;
              for (int j = 0; j < 8; ++j)
                  crc = (crc & 0x80) != 0 ? (crc << 1) ^ shpoly : crc << 1;
              table[i] = (byte) ((crc >> (8 - bitWidth)) & widthMask);
          }
      }
  
      @Override
      protected int resumeRaw(int crc, byte[] input, int index, int length) {
          for (int i = 0; i < length; ++i)
              crc = table[(crc << (8 - bitWidth)) ^ (input[index + i] & 0xff)] & 0xff;
          return crc;
      }
  }
  