/*
 * Copyright (c) 2011 ymnk, JCraft,Inc. 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. The names of the authors may not be used to endorse or promote products derived from this
 * software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED 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 JCRAFT, INC. OR ANY CONTRIBUTORS TO THIS SOFTWARE 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 program is based on zlib-1.1.3, so all credit should go authors Jean-loup
 * Gailly(jloup@gzip.org) and Mark Adler(madler@alumni.caltech.edu) and contributors of zlib.
 */

package com.jcraft.jsch.jzlib;

final class CRC32 implements Checksum {

  /*
   * The following logic has come from RFC1952.
   */
  private int v = 0;
  private static int[] crc_table = null;

  static {
    crc_table = new int[256];
    for (int n = 0; n < 256; n++) {
      int c = n;
      for (int k = 8; --k >= 0;) {
        if ((c & 1) != 0)
          c = 0xedb88320 ^ (c >>> 1);
        else
          c = c >>> 1;
      }
      crc_table[n] = c;
    }
  }

  @Override
  public void update(byte[] buf, int index, int len) {
    int c = ~v;
    while (--len >= 0)
      c = crc_table[(c ^ buf[index++]) & 0xff] ^ (c >>> 8);
    v = ~c;
  }

  @Override
  public void reset() {
    v = 0;
  }

  @Override
  public void reset(long vv) {
    v = (int) (vv & 0xffffffffL);
  }

  @Override
  public long getValue() {
    return v & 0xffffffffL;
  }

  // The following logic has come from zlib.1.2.
  private static final int GF2_DIM = 32;

  static long combine(long crc1, long crc2, long len2) {
    long row;
    long[] even = new long[GF2_DIM];
    long[] odd = new long[GF2_DIM];

    // degenerate case (also disallow negative lengths)
    if (len2 <= 0)
      return crc1;

    // put operator for one zero bit in odd
    odd[0] = 0xedb88320L; // CRC-32 polynomial
    row = 1;
    for (int n = 1; n < GF2_DIM; n++) {
      odd[n] = row;
      row <<= 1;
    }

    // put operator for two zero bits in even
    gf2_matrix_square(even, odd);

    // put operator for four zero bits in odd
    gf2_matrix_square(odd, even);

    // apply len2 zeros to crc1 (first square will put the operator for one
    // zero byte, eight zero bits, in even)
    do {
      // apply zeros operator for this bit of len2
      gf2_matrix_square(even, odd);
      if ((len2 & 1) != 0)
        crc1 = gf2_matrix_times(even, crc1);
      len2 >>= 1;

      // if no more bits set, then done
      if (len2 == 0)
        break;

      // another iteration of the loop with odd and even swapped
      gf2_matrix_square(odd, even);
      if ((len2 & 1) != 0)
        crc1 = gf2_matrix_times(odd, crc1);
      len2 >>= 1;

      // if no more bits set, then done
    } while (len2 != 0);

    /* return combined crc */
    crc1 ^= crc2;
    return crc1;
  }

  private static long gf2_matrix_times(long[] mat, long vec) {
    long sum = 0;
    int index = 0;
    while (vec != 0) {
      if ((vec & 1) != 0)
        sum ^= mat[index];
      vec >>= 1;
      index++;
    }
    return sum;
  }

  static final void gf2_matrix_square(long[] square, long[] mat) {
    for (int n = 0; n < GF2_DIM; n++)
      square[n] = gf2_matrix_times(mat, mat[n]);
  }

  /*
  private java.util.zip.CRC32 crc32 = new java.util.zip.CRC32();

  void update(byte[] buf, int index, int len) {
    if (buf == null) { crc32.reset(); }
    else { crc32.update(buf, index, len); }
  }
  void reset() {
    crc32.reset();
  }
  void reset(long init) {
    if (init == 0L) {
      crc32.reset();
    } else {
      System.err.println("unsupported operation");
    }
  }
  long getValue() {
    return crc32.getValue();
  }
  */
  @Override
  public CRC32 copy() {
    CRC32 foo = new CRC32();
    foo.v = this.v;
    return foo;
  }

  static int[] getCRC32Table() {
    int[] tmp = new int[crc_table.length];
    System.arraycopy(crc_table, 0, tmp, 0, tmp.length);
    return tmp;
  }
}
