/*


  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;

/**
 * A class that can be used to compute the Cksum of a data stream.
 * This is a 100% Java implementation.
 */

// implemented in Java from original GNU C source
// it computes a POSIX 1003.2 checksum.
public class Cksum extends AbstractChecksum {
    protected int value;

    protected final int[] crctab = {
        0x00000000,
        0x04C11DB7, 0x09823B6E, 0x0D4326D9, 0x130476DC, 0x17C56B6B,
        0x1A864DB2, 0x1E475005, 0x2608EDB8, 0x22C9F00F, 0x2F8AD6D6,
        0x2B4BCB61, 0x350C9B64, 0x31CD86D3, 0x3C8EA00A, 0x384FBDBD,
        0x4C11DB70, 0x48D0C6C7, 0x4593E01E, 0x4152FDA9, 0x5F15ADAC,
        0x5BD4B01B, 0x569796C2, 0x52568B75, 0x6A1936C8, 0x6ED82B7F,
        0x639B0DA6, 0x675A1011, 0x791D4014, 0x7DDC5DA3, 0x709F7B7A,
        0x745E66CD, 0x9823B6E0, 0x9CE2AB57, 0x91A18D8E, 0x95609039,
        0x8B27C03C, 0x8FE6DD8B, 0x82A5FB52, 0x8664E6E5, 0xBE2B5B58,
        0xBAEA46EF, 0xB7A96036, 0xB3687D81, 0xAD2F2D84, 0xA9EE3033,
        0xA4AD16EA, 0xA06C0B5D, 0xD4326D90, 0xD0F37027, 0xDDB056FE,
        0xD9714B49, 0xC7361B4C, 0xC3F706FB, 0xCEB42022, 0xCA753D95,
        0xF23A8028, 0xF6FB9D9F, 0xFBB8BB46, 0xFF79A6F1, 0xE13EF6F4,
        0xE5FFEB43, 0xE8BCCD9A, 0xEC7DD02D, 0x34867077, 0x30476DC0,
        0x3D044B19, 0x39C556AE, 0x278206AB, 0x23431B1C, 0x2E003DC5,
        0x2AC12072, 0x128E9DCF, 0x164F8078, 0x1B0CA6A1, 0x1FCDBB16,
        0x018AEB13, 0x054BF6A4, 0x0808D07D, 0x0CC9CDCA, 0x7897AB07,
        0x7C56B6B0, 0x71159069, 0x75D48DDE, 0x6B93DDDB, 0x6F52C06C,
        0x6211E6B5, 0x66D0FB02, 0x5E9F46BF, 0x5A5E5B08, 0x571D7DD1,
        0x53DC6066, 0x4D9B3063, 0x495A2DD4, 0x44190B0D, 0x40D816BA,
        0xACA5C697, 0xA864DB20, 0xA527FDF9, 0xA1E6E04E, 0xBFA1B04B,
        0xBB60ADFC, 0xB6238B25, 0xB2E29692, 0x8AAD2B2F, 0x8E6C3698,
        0x832F1041, 0x87EE0DF6, 0x99A95DF3, 0x9D684044, 0x902B669D,
        0x94EA7B2A, 0xE0B41DE7, 0xE4750050, 0xE9362689, 0xEDF73B3E,
        0xF3B06B3B, 0xF771768C, 0xFA325055, 0xFEF34DE2, 0xC6BCF05F,
        0xC27DEDE8, 0xCF3ECB31, 0xCBFFD686, 0xD5B88683, 0xD1799B34,
        0xDC3ABDED, 0xD8FBA05A, 0x690CE0EE, 0x6DCDFD59, 0x608EDB80,
        0x644FC637, 0x7A089632, 0x7EC98B85, 0x738AAD5C, 0x774BB0EB,
        0x4F040D56, 0x4BC510E1, 0x46863638, 0x42472B8F, 0x5C007B8A,
        0x58C1663D, 0x558240E4, 0x51435D53, 0x251D3B9E, 0x21DC2629,
        0x2C9F00F0, 0x285E1D47, 0x36194D42, 0x32D850F5, 0x3F9B762C,
        0x3B5A6B9B, 0x0315D626, 0x07D4CB91, 0x0A97ED48, 0x0E56F0FF,
        0x1011A0FA, 0x14D0BD4D, 0x19939B94, 0x1D528623, 0xF12F560E,
        0xF5EE4BB9, 0xF8AD6D60, 0xFC6C70D7, 0xE22B20D2, 0xE6EA3D65,
        0xEBA91BBC, 0xEF68060B, 0xD727BBB6, 0xD3E6A601, 0xDEA580D8,
        0xDA649D6F, 0xC423CD6A, 0xC0E2D0DD, 0xCDA1F604, 0xC960EBB3,
        0xBD3E8D7E, 0xB9FF90C9, 0xB4BCB610, 0xB07DABA7, 0xAE3AFBA2,
        0xAAFBE615, 0xA7B8C0CC, 0xA379DD7B, 0x9B3660C6, 0x9FF77D71,
        0x92B45BA8, 0x9675461F, 0x8832161A, 0x8CF30BAD, 0x81B02D74,
        0x857130C3, 0x5D8A9099, 0x594B8D2E, 0x5408ABF7, 0x50C9B640,
        0x4E8EE645, 0x4A4FFBF2, 0x470CDD2B, 0x43CDC09C, 0x7B827D21,
        0x7F436096, 0x7200464F, 0x76C15BF8, 0x68860BFD, 0x6C47164A,
        0x61043093, 0x65C52D24, 0x119B4BE9, 0x155A565E, 0x18197087,
        0x1CD86D30, 0x029F3D35, 0x065E2082, 0x0B1D065B, 0x0FDC1BEC,
        0x3793A651, 0x3352BBE6, 0x3E119D3F, 0x3AD08088, 0x2497D08D,
        0x2056CD3A, 0x2D15EBE3, 0x29D4F654, 0xC5A92679, 0xC1683BCE,
        0xCC2B1D17, 0xC8EA00A0, 0xD6AD50A5, 0xD26C4D12, 0xDF2F6BCB,
        0xDBEE767C, 0xE3A1CBC1, 0xE760D676, 0xEA23F0AF, 0xEEE2ED18,
        0xF0A5BD1D, 0xF464A0AA, 0xF9278673, 0xFDE69BC4, 0x89B8FD09,
        0x8D79E0BE, 0x803AC667, 0x84FBDBD0, 0x9ABC8BD5, 0x9E7D9662,
        0x933EB0BB, 0x97FFAD0C, 0xAFB010B1, 0xAB710D06, 0xA6322BDF,
        0xA2F33668, 0xBCB4666D, 0xB8757BDA, 0xB5365D03, 0xB1F740B4
    };

    public Cksum() {
        super();
        bitWidth = 32;
        value = 0;
        length = 0;
        formatPreferences.setHashEncoding(Encoding.DEC);
        formatPreferences.setFilesizeWanted(true);
        formatPreferences.setSeparator(" ");
    }

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

    @Override
    public void update(byte[] bytes, int offset, int length) {
        for (int i = offset; i < length + offset; i++) {
            value = (value << 8) ^ crctab[ ((value >> 24) ^ bytes[i]) & 0xFF];
        }
        this.length += length;
    }

    // a 2.5 GB file (length=2684354560), filled with random
    // bytes (Java seed=0), returns a cksum value of 128656372
    @Override
    public long getValue() {

        // store both length and value to temp variables,
        // so we can launch getValue() multiple times
        long tmpLength = length;
        int tmpValue = value;

        // include the length of the file to the checksum value
        for (; tmpLength != 0; tmpLength >>= 8) {
            tmpValue = (tmpValue << 8) ^ crctab[((tmpValue >> 24) ^ (int)(tmpLength & 0xFF)) & 0xFF];
        }

        return (~tmpValue & 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)};
    }

}
