How to convert this crc16 C implementation to java?

Question

Hi I have this C crc16 implementation:

const unsigned short CRCtbl[ 256 ] =
{
    0x0000, 0xC0C1, 0xC181, 0x0140, 0xC301, 0x03C0, 0x0280, 0xC241,
    0xC601, 0x06C0, 0x0780, 0xC741, 0x0500, 0xC5C1, 0xC481, 0x0440,
    0xCC01, 0x0CC0, 0x0D80, 0xCD41, 0x0F00, 0xCFC1, 0xCE81, 0x0E40,
    0x0A00, 0xCAC1, 0xCB81, 0x0B40, 0xC901, 0x09C0, 0x0880, 0xC841,
    0xD801, 0x18C0, 0x1980, 0xD941, 0x1B00, 0xDBC1, 0xDA81, 0x1A40,
    0x1E00, 0xDEC1, 0xDF81, 0x1F40, 0xDD01, 0x1DC0, 0x1C80, 0xDC41,
    0x1400, 0xD4C1, 0xD581, 0x1540, 0xD701, 0x17C0, 0x1680, 0xD641,
    0xD201, 0x12C0, 0x1380, 0xD341, 0x1100, 0xD1C1, 0xD081, 0x1040,
    0xF001, 0x30C0, 0x3180, 0xF141, 0x3300, 0xF3C1, 0xF281, 0x3240,
    0x3600, 0xF6C1, 0xF781, 0x3740, 0xF501, 0x35C0, 0x3480, 0xF441,
    0x3C00, 0xFCC1, 0xFD81, 0x3D40, 0xFF01, 0x3FC0, 0x3E80, 0xFE41,
    0xFA01, 0x3AC0, 0x3B80, 0xFB41, 0x3900, 0xF9C1, 0xF881, 0x3840,
    0x2800, 0xE8C1, 0xE981, 0x2940, 0xEB01, 0x2BC0, 0x2A80, 0xEA41,
    0xEE01, 0x2EC0, 0x2F80, 0xEF41, 0x2D00, 0xEDC1, 0xEC81, 0x2C40,
    0xE401, 0x24C0, 0x2580, 0xE541, 0x2700, 0xE7C1, 0xE681, 0x2640,
    0x2200, 0xE2C1, 0xE381, 0x2340, 0xE101, 0x21C0, 0x2080, 0xE041,
    0xA001, 0x60C0, 0x6180, 0xA141, 0x6300, 0xA3C1, 0xA281, 0x6240,
    0x6600, 0xA6C1, 0xA781, 0x6740, 0xA501, 0x65C0, 0x6480, 0xA441,
    0x6C00, 0xACC1, 0xAD81, 0x6D40, 0xAF01, 0x6FC0, 0x6E80, 0xAE41,
    0xAA01, 0x6AC0, 0x6B80, 0xAB41, 0x6900, 0xA9C1, 0xA881, 0x6840,
    0x7800, 0xB8C1, 0xB981, 0x7940, 0xBB01, 0x7BC0, 0x7A80, 0xBA41,
    0xBE01, 0x7EC0, 0x7F80, 0xBF41, 0x7D00, 0xBDC1, 0xBC81, 0x7C40,
    0xB401, 0x74C0, 0x7580, 0xB541, 0x7700, 0xB7C1, 0xB681, 0x7640,
    0x7200, 0xB2C1, 0xB381, 0x7340, 0xB101, 0x71C0, 0x7080, 0xB041,
    0x5000, 0x90C1, 0x9181, 0x5140, 0x9301, 0x53C0, 0x5280, 0x9241,
    0x9601, 0x56C0, 0x5780, 0x9741, 0x5500, 0x95C1, 0x9481, 0x5440,
    0x9C01, 0x5CC0, 0x5D80, 0x9D41, 0x5F00, 0x9FC1, 0x9E81, 0x5E40,
    0x5A00, 0x9AC1, 0x9B81, 0x5B40, 0x9901, 0x59C0, 0x5880, 0x9841,
    0x8801, 0x48C0, 0x4980, 0x8941, 0x4B00, 0x8BC1, 0x8A81, 0x4A40,
    0x4E00, 0x8EC1, 0x8F81, 0x4F40, 0x8D01, 0x4DC0, 0x4C80, 0x8C41,
    0x4400, 0x84C1, 0x8581, 0x4540, 0x8701, 0x47C0, 0x4680, 0x8641,
    0x8201, 0x42C0, 0x4380, 0x8341, 0x4100, 0x81C1, 0x8081,
    0x4040
};

unsigned short Crc_16(unsigned char *str, int n)
{
    unsigned short crc = 0xFFFF;
    do
    {
        crc = ( crc >> 8 ) ^ CRCtbl[ ( crc & 0xFF ) ^ *str ];
        str++;
    }
    while(--n);
    return(crc);
}

I need to convert it into java one. My problem is that,since java does not provide unsigned int type, the implementation fails in some cases (some info[] byte >127 when considering it as unsigned).

private int crc_xor(byte[] info) {
    int[] table = {
            0x0000 ,0xC0C1 ,0xC181 ,0x0140 ,0xC301 ,0x03C0 ,0x0280 ,0xC241,
            0xC601 ,0x06C0 ,0x0780 ,0xC741 ,0x0500 ,0xC5C1 ,0xC481 ,0x0440,
            0xCC01 ,0x0CC0 ,0x0D80 ,0xCD41 ,0x0F00 ,0xCFC1 ,0xCE81 ,0x0E40,
            0x0A00 ,0xCAC1 ,0xCB81 ,0x0B40 ,0xC901 ,0x09C0 ,0x0880 ,0xC841,
            0xD801 ,0x18C0 ,0x1980 ,0xD941 ,0x1B00 ,0xDBC1 ,0xDA81 ,0x1A40,
            0x1E00 ,0xDEC1 ,0xDF81 ,0x1F40 ,0xDD01 ,0x1DC0 ,0x1C80 ,0xDC41,
            0x1400 ,0xD4C1 ,0xD581 ,0x1540 ,0xD701 ,0x17C0 ,0x1680 ,0xD641,
            0xD201 ,0x12C0 ,0x1380 ,0xD341 ,0x1100 ,0xD1C1 ,0xD081 ,0x1040,
            0xF001 ,0x30C0 ,0x3180 ,0xF141 ,0x3300 ,0xF3C1 ,0xF281 ,0x3240,
            0x3600 ,0xF6C1 ,0xF781 ,0x3740 ,0xF501 ,0x35C0 ,0x3480 ,0xF441,
            0x3C00 ,0xFCC1 ,0xFD81 ,0x3D40 ,0xFF01 ,0x3FC0 ,0x3E80 ,0xFE41,
            0xFA01 ,0x3AC0 ,0x3B80 ,0xFB41 ,0x3900 ,0xF9C1 ,0xF881 ,0x3840,
            0x2800 ,0xE8C1 ,0xE981 ,0x2940 ,0xEB01 ,0x2BC0 ,0x2A80 ,0xEA41,
            0xEE01 ,0x2EC0 ,0x2F80 ,0xEF41 ,0x2D00 ,0xEDC1 ,0xEC81 ,0x2C40,
            0xE401 ,0x24C0 ,0x2580 ,0xE541 ,0x2700 ,0xE7C1 ,0xE681 ,0x2640,
            0x2200 ,0xE2C1 ,0xE381 ,0x2340 ,0xE101 ,0x21C0 ,0x2080 ,0xE041,
            0xA001 ,0x60C0 ,0x6180 ,0xA141 ,0x6300 ,0xA3C1 ,0xA281 ,0x6240,
            0x6600 ,0xA6C1 ,0xA781 ,0x6740 ,0xA501 ,0x65C0 ,0x6480 ,0xA441,
            0x6C00 ,0xACC1 ,0xAD81 ,0x6D40 ,0xAF01 ,0x6FC0 ,0x6E80 ,0xAE41,
            0xAA01 ,0x6AC0 ,0x6B80 ,0xAB41 ,0x6900 ,0xA9C1 ,0xA881 ,0x6840,
            0x7800 ,0xB8C1 ,0xB981 ,0x7940 ,0xBB01 ,0x7BC0 ,0x7A80 ,0xBA41,
            0xBE01 ,0x7EC0 ,0x7F80 ,0xBF41 ,0x7D00 ,0xBDC1 ,0xBC81 ,0x7C40,
            0xB401 ,0x74C0 ,0x7580 ,0xB541 ,0x7700 ,0xB7C1 ,0xB681 ,0x7640,
            0x7200 ,0xB2C1 ,0xB381 ,0x7340 ,0xB101 ,0x71C0 ,0x7080 ,0xB041,
            0x5000 ,0x90C1 ,0x9181 ,0x5140 ,0x9301 ,0x53C0 ,0x5280 ,0x9241,
            0x9601 ,0x56C0 ,0x5780 ,0x9741 ,0x5500 ,0x95C1 ,0x9481 ,0x5440,
            0x9C01 ,0x5CC0 ,0x5D80 ,0x9D41 ,0x5F00 ,0x9FC1 ,0x9E81 ,0x5E40,
            0x5A00 ,0x9AC1 ,0x9B81 ,0x5B40 ,0x9901 ,0x59C0 ,0x5880 ,0x9841,
            0x8801 ,0x48C0 ,0x4980 ,0x8941 ,0x4B00 ,0x8BC1 ,0x8A81 ,0x4A40,
            0x4E00 ,0x8EC1 ,0x8F81 ,0x4F40 ,0x8D01 ,0x4DC0 ,0x4C80 ,0x8C41,
            0x4400 ,0x84C1 ,0x8581 ,0x4540 ,0x8701 ,0x47C0 ,0x4680 ,0x8641,
            0x8201 ,0x42C0 ,0x4380 ,0x8341 ,0x4100 ,0x81C1 ,0x8081 ,0x4040};

            int crc16=0;
            int pos=0;
            int lungh=info.length;

            lungh-=1;

            while(lungh>=0)
            {
                crc16 = ((crc16 >> 8) ^ table[(crc16&0xFF) ^ info[pos]]) & 0xFFFF;
                pos+=1;
                lungh-=1;

            }

            return crc16;
}

There are many java crc16 implementations but not this (used in SIA standard). Can you help me? thanks

Help you do what? SO isn't for generalized help, it's for answering questions, and you haven't asked anything specific. Read this: [Why is "Can someone help me?" not an actual question?](http://meta.stackoverflow.com/questions/284236/why-is-can-someone-help-me-not-an-actual-question). — azurefrog, Mar 07 '16 at 15:35
the question is how to manage in a correct way this specific crc16 implementation in java... — SUPERALEX, Mar 07 '16 at 16:06
What have you tried this far? The source you provided is C, and it should be fairly easy to turn into Java. It might be a good idea for you to try to write it in Java and then ask specific questions about parts you have difficulties with. — , Mar 07 '16 at 16:29
Are you sure there is not an existing CRC-16 library? If it is true CRC-16 then you can use an existing CRC-16 library and set the correct polynomial for the variant used. — rve, Mar 07 '16 at 17:51
@SamiLaine maybe you didn't see but in the question i put my java conversion below C version..This version works till,as i wrote, the bytes are < 127,viceversa it crashes because java thinks they are signed... — SUPERALEX, Mar 07 '16 at 20:29

score 0 · Accepted Answer · answered Mar 08 '16 at 01:14

0

Try changing the (crc16&0xFF) ^ info[pos] to (crc16 ^ info[pos])&0xFF.

answered Mar 08 '16 at 01:14

Mark Adler

101,978
13
118
158

seems to work!! thanks – SUPERALEX Mar 08 '16 at 08:43
im sorry but the C version crc is different...with this packet 02 21 43 65 10 03 02 00 02 the C crc results in 47 8B but java version prints 07 80... – SUPERALEX Mar 15 '16 at 16:54
I can't get either of those CRCs from that "packet", no matter how I interpret it. Is it supposed to be hex? Decimal? ASCII digits with spaces? What? – Mark Adler Mar 16 '16 at 02:04
ok your solution works there was an error in java code..the crc was initialized with 0 but in C was 0XFFFF....so the correct code is `int crc16=0xFFFF; ecc` – SUPERALEX Mar 16 '16 at 09:33

How to convert this crc16 C implementation to java?

1 Answers1