CRC 4 implementation for C #

Question

Solved by this code -> https://gist.github.com/Sbreitzke/b26107798eee74e39ff85800abf71fb1

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I searched the internet for implementing CRC 4 in C # because I need to calculate the checksum

Change the barcode numbers in hexadecimal notation, then bytes and then bits, and then calculate the CRC4 checksum in the bit stream.

I already found this question 8 years ago with no CRC-4 answer in C # .

I tried changing CRC 8 and 16 implementations to CRC 4, but they do not quite get the desired result.

0130E0928270FFFFFFFmust be rated before 7.

I found two implementations of C, but could not convert them to C #. For example, this one:

 short[] crc4_tab = {
 0x0, 0x7, 0xe, 0x9, 0xb, 0xc, 0x5, 0x2,
 0x1, 0x6, 0xf, 0x8, 0xa, 0xd, 0x4, 0x3,
};

/**
* crc4 - calculate the 4-bit crc of a value.
* @crc:  starting crc4
* @x:    value to checksum
* @bits: number of bits in @x to checksum
*
* Returns the crc4 value of @x, using polynomial 0b10111.
*
* The @x value is treated as left-aligned, and bits above @bits are ignored
* in the crc calculations.
*/
short crc4(uint8_t c, uint64_t x, int bits)
{
    int i;

    /* mask off anything above the top bit */
    x &= (1ull << bits) -1;

    /* Align to 4-bits */
    bits = (bits + 3) & ~0x3;

    /* Calculate crc4 over four-bit nibbles, starting at the MSbit */
    for (i = bits - 4; i >= 0; i -= 4)
    c = crc4_tab[c ^ ((x >> i) & 0xf)];

    return c;
}

My current generation code (unit test) is as follows:

[TestMethod]
public void x()
{
    var ordnungskennzeichen = 01;
    var kundennummer = 51251496;
    var einlieferungsbel = 9999;
    var sendungsnr = 16777215;

    var hex_ordnungskennzeichen = ordnungskennzeichen.ToString("x2");
    var hex_kundennummer = kundennummer.ToString("x2");
    var hex_einlieferungsbel = einlieferungsbel.ToString("x2");
    var hex_sendungsnr = sendungsnr.ToString("x2");

    var complete = hex_ordnungskennzeichen + hex_kundennummer + hex_einlieferungsbel + hex_sendungsnr;

    var bytes = Encoding.ASCII.GetBytes(complete);

    //var computeChecksum = crc4(???);
    //   Console.WriteLine(computeChecksum);

}

short[] crc4_tab = {
    0x0, 0x7, 0xe, 0x9, 0xb, 0xc, 0x5, 0x2,
    0x1, 0x6, 0xf, 0x8, 0xa, 0xd, 0x4, 0x3,
};

/**
* crc4 - calculate the 4-bit crc of a value.
* @crc:  starting crc4
* @x:    value to checksum
* @bits: number of bits in @x to checksum
*
* Returns the crc4 value of @x, using polynomial 0b10111.
*
* The @x value is treated as left-aligned, and bits above @bits are ignored
* in the crc calculations.
*/

short crc4(byte c, ulong x, int bits)
{
    int i;

    /* mask off anything above the top bit */
    x &= ((ulong)1 << bits) -1;

    /* Align to 4-bits */
    bits = (bits + 3) & ~0x3;

    /* Calculate crc4 over four-bit nibbles, starting at the MSbit */
    for (i = bits - 4; i >= 0; i -= 4)
        c = (byte) crc4_tab[c ^ ((x >> i) & 0xf)];

    return c;
}

Answer 1

Deutsche Post AG ( , Deutsche Post):

https://gist.github.com/Sbreitzke/b26107798eee74e39ff85800abf71fb1

Answer 2

# . c - (4- ), x - 64- , crc4, bits - 64- , ( ). - 64- x - . , , , 64- , bits 4. , :

static readonly byte[] crc4_tab = {
    0x0, 0x7, 0xe, 0x9, 0xb, 0xc, 0x5, 0x2,
    0x1, 0x6, 0xf, 0x8, 0xa, 0xd, 0x4, 0x3,
};

static byte crc4(byte c, byte x) {
    var low4Bits = x & 0x0F;
    var high4Bits = x >> 4;
    c = crc4_tab[c ^ high4Bits];
    c = crc4_tab[c ^ low4Bits];

    return c;
}

static byte crc4(byte[] array) {
    byte start = 0;
    foreach (var item in array) {
        start = crc4(start, item);
    }
    return start;
}