/*


  Jacksum 3.6.0 - a checksum utility in Java
  Copyright (c) 2001-2023 Dipl.-Inf. (FH) Johann N. Löfflmann,
  All Rights Reserved, <https://jacksum.net>.

  This program is free software: you can redistribute it and/or modify it under
  the terms of the GNU General Public License as published by the Free Software
  Foundation, either version 3 of the License, or (at your option) any later
  version.

  This program 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 General Public License for more
  details.

  You should have received a copy of the GNU General Public License along with
  this program. If not, see <https://www.gnu.org/licenses/>.


 */

package net.jacksum.algorithms.checksums;

import net.jacksum.algorithms.AbstractChecksum;
import net.jacksum.formats.Encoding;

/* from the C source code ... */
/* cksum.c - Display file checksums and block counts    Author: V. Archer */
/* Copyright 1991 by Vincent Archer
 *      You may freely redistribute this software, in source or binary
 *      form, provided that you do not alter this copyright mention in any
 *      way.
 */

/* Cksum_minix.java - converted from cksum.c to Java
   Author: Johann N. Loefflmann */
/* Copyright 2008 by Johann N. Loefflmann
 *      Released under the GPL
 */

public class Cksum_Minix extends AbstractChecksum {
    protected int value;

    protected final int[] crctab = {
/* Table from P1003.2 (4.9/Fig 4.1). In fact, this table was taken from zmodem
 * and rewritten to look like the Draft 11 example.
 */
          0x7fffffff,
          0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419, 0x706af48f,
          0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4, 0xe0d5e91e,
          0x97d2d988, 0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91,
          0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de, 0x1adad47d,
          0x6ddde4eb, 0xf4d4b551, 0x83d385c7, 0x136c9856, 0x646ba8c0,
          0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9, 0xfa0f3d63,
          0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172,
          0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b, 0x35b5a8fa,
          0x42b2986c, 0xdbbbc9d6, 0xacbcf940, 0x32d86ce3, 0x45df5c75,
          0xdcd60dcf, 0xabd13d59, 0x26d930ac, 0x51de003a, 0xc8d75180,
          0xbfd06116, 0x21b4f4b5, 0x56b3c423, 0xcfba9599, 0xb8bda50f,
          0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924, 0x2f6f7c87,
          0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190, 0x01db7106,
          0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f, 0x9fbfe4a5,
          0xe8b8d433, 0x7807c9a2, 0x0f00f934, 0x9609a88e, 0xe10e9818,
          0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01, 0x6b6b51f4,
          0x1c6c6162, 0x856530d8, 0xf262004e, 0x6c0695ed, 0x1b01a57b,
          0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950, 0x8bbeb8ea,
          0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65,
          0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2, 0x4adfa541,
          0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a, 0x346ed9fc,
          0xad678846, 0xda60b8d0, 0x44042d73, 0x33031de5, 0xaa0a4c5f,
          0xdd0d7cc9, 0x5005713c, 0x270241aa, 0xbe0b1010, 0xc90c2086,
          0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f, 0x5edef90e,
          0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17, 0x2eb40d81,
          0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6, 0x03b6e20c,
          0x74b1d29a, 0xead54739, 0x9dd277af, 0x04db2615, 0x73dc1683,
          0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8, 0xe40ecf0b,
          0x9309ff9d, 0x0a00ae27, 0x7d079eb1, 0xf00f9344, 0x8708a3d2,
          0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb, 0x196c3671,
          0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc,
          0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5, 0xd6d6a3e8,
          0xa1d1937e, 0x38d8c2c4, 0x4fdff252, 0xd1bb67f1, 0xa6bc5767,
          0x3fb506dd, 0x48b2364b, 0xd80d2bda, 0xaf0a1b4c, 0x36034af6,
          0x41047a60, 0xdf60efc3, 0xa867df55, 0x316e8eef, 0x4669be79,
          0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236, 0xcc0c7795,
          0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe, 0xb2bd0b28,
          0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31, 0x2cd99e8b,
          0x5bdeae1d, 0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x026d930a,
          0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713, 0x95bf4a82,
          0xe2b87a14, 0x7bb12bae, 0x0cb61b38, 0x92d28e9b, 0xe5d5be0d,
          0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242, 0x68ddb3f8,
          0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777,
          0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c, 0x8f659eff,
          0xf862ae69, 0x616bffd3, 0x166ccf45, 0xa00ae278, 0xd70dd2ee,
          0x4e048354, 0x3903b3c2, 0xa7672661, 0xd06016f7, 0x4969474d,
          0x3e6e77db, 0xaed16a4a, 0xd9d65adc, 0x40df0b66, 0x37d83bf0,
          0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9, 0xbdbdf21c,
          0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605, 0xcdd70693,
          0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8, 0x5d681b02,
          0x2a6f2b94, 0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d
    };

    public Cksum_Minix() {
        super();
        bitWidth = 32;
        formatPreferences.setHashEncoding(Encoding.DEC);
        formatPreferences.setSeparator(" ");
    }

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

    private int aux = 0;

    @Override
    public void update(byte[] bytes, int offset, int length) {
        for (int i = offset; i < length + offset; i++) {

            /* Compute the index to the crc table */
            int index = ((value >> 24) ^ bytes[i]) & 0xFF;

            /* Replace an intermediate zero with the next value
             * from the sequence */
            if (index == 0) {
                index = aux++;
                if (aux >= 256) aux = 0;
            }

            /* New checksum value */
            value = (value << 8) ^ crctab[index];

        }
        this.length += length;
    }

    @Override
    public long getValue() {
        return (value & 0xFFFFFFFFL);
    }

    @Override
    public byte[] getByteArray() {
        long val = getValue();
        return new byte[]
        {(byte)((val>>24)&0xff),
         (byte)((val>>16)&0xff),
         (byte)((val>>8)&0xff),
         (byte)(val&0xff)};
    }

}
