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/*
 * Copyright 2023 the original author or authors.
 *
 * 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 org.seppiko.commons.utils.crypto;

import java.util.zip.Checksum;

/**
 * A class that can be used to compute the CRC64 of a data stream with ECMA182.
 *
 * @see 
 *   Cyclic redundancy check(CRC)
 * @see ECMA-182
 * @author Leonard Woo
 */
public class CRC64ECMA182 implements Checksum {

  private static final long ECMA182INIT = 0;
  private static final long ECMA182POLY = 0xC96C5795D7870F42L;

  private static final int TABLE_LENGTH = 0x100;
  private static final long[] table;

  static {
    // Generator table
    table = new long[TABLE_LENGTH];

    for (int n = 0; n < TABLE_LENGTH; n++) {
      long crc = n;
      for (int k = 0; k < 8; k++) {
        crc = ((crc & 1) == 1) ? ((crc >>> 1) ^ ECMA182POLY) : (crc >>> 1);
      }
      table[n] = crc;
    }
  }

  private long crc;

  /** Create CRC64 object and initialization. */
  public CRC64ECMA182() {
    crc = ECMA182INIT;
  }

  /**
   * Updates the CRC64 checksum with the specified byte.
   *
   * @param b number.
   */
  @Override
  public void update(int b) {
    updateByte((byte) (b & 0xFF));
  }

  /**
   * Updates the CRC64 checksum with the specified array of bytes.
   *
   * @param b data byte array.
   * @param off data init offset.
   * @param len data length.
   * @throws NullPointerException data is {@code null}.
   * @throws ArrayIndexOutOfBoundsException if off is negative, or len is negative, or off+len is *
   *     negative or greater than the length of the array b.
   */
  @Override
  public void update(byte[] b, int off, int len)
      throws NullPointerException, ArrayIndexOutOfBoundsException {
    updateCheck(b, off, len);
    for (int i = off; len > 0; i++, len--) {
      updateByte(b[i]);
    }
  }

  // calc exec
  private void updateByte(final byte b) {
    crc = ~crc;
    crc = (crc >>> 8) ^ table[((int) (crc ^ b)) & 0xFF];
    crc = ~crc;
  }

  private void updateCheck(byte[] b, int off, int len)
      throws NullPointerException, ArrayIndexOutOfBoundsException {
    if (b == null) {
      throw new NullPointerException();
    }
    if (off < 0 || len < 0 || off > (b.length - len)) {
      throw new ArrayIndexOutOfBoundsException();
    }
  }

  /**
   * Returns CRC64 value.
   *
   * @return CRC64 value.
   */
  @Override
  public long getValue() {
    return crc;
  }

  /** Resets CRC64 to initial value. */
  @Override
  public void reset() {
    crc = ECMA182INIT;
  }
}