POSIX cksum algorithm in Java

Most Unix programs rely on cksum for checking duplicate files. If you happen to migrate programs doing that, you need to make sure that you’ll be using the same algorithm for the same functionality of course.

Here is the [cksum algorithm] and here is the [cksum man] page.

The class below is implementing the java.util.zip.Checksum interface for extensibility.

/**
 * Compute the checksum of a data stream using the
 * POSIX cksum algorithm.
 */
public class Cksum implements Checksum {
	
    /**
     * The checksum value.
     */
    private int value;
	
    /**
     * The length of the stream.
     */
    private int length;
	
    /**
     * The cksum payload.
     */
    private final int[] payload = {
        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
    };
	
    /**
     * Checksum constructor, reset checksum.
     */
    public Cksum() {
        super();
        reset();
    }
	
    /**
     * Reset the checksum.
     */
    public final void reset() {
        value = 0;
        length = 0;
    }
	
    /**
     * Update checksum value using a byte.
     *
     * @param byteRead is the byte read to include in the computation.
     */
    public void update(final byte byteRead) {
        value = (value << 8 ) ^ payload[ ((value >> 24) ^ byteRead)   & 0xFF];
        length++;
    }
	
    /**
     * Update checksum value using an int.
     *
     * @param byteRead is the byte read in int form to include in the computation.
     */
    public void update(final int byteRead) {
        update((byte)(byteRead & 0xFF));
    }
	
    /**
     * Get the cksum checksum value.
     * a 2.5 GB file (length=2684354560), filled with random
     * bytes (Java seed=0), returns a cksum value of 128656372
     *
     * @return the cksum value.
     */
    public final long getValue() {
	
        // store both length and value to temps,
        // 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 ) ^ payload[((tmpValue >> 24) ^ (int)(tmpLength & 0xFF)) & 0xFF];
        }
	
        return (~tmpValue & 0xFFFFFFFFL);
    }
	
    /**
     * Get the size of the stream.
     *
     * @return the size of the stream in bytes.
     */
    public final long getLength() {
        return length;
    }
	
    /**
     * Get the value in byte array form.
     *
     * @return the checksum value in byte array form.
     */
    public final byte[] getByteArray() {
        final long localValue = getValue();
        return new byte[]
        {(byte)((localValue >> 24)&0xff),
         (byte)((localValue >> 16)&0xff),
         (byte)((localValue >> 8 )&0xff),
         (byte)(localValue&0xff)};
    }
	
    /**
     * Method to work with java.util.zip.Checksum calls.
     */
    @Override
    public void update(final byte[] b, final int off, final int len) {
        for (int i = off; i < len + off; i++) {
            update(b[i]);
        }
    }
}