Read a packed decimal (Comp-3) number value which is 8 characters; but holds a 13 digit number and convert to 13 digits numeric value

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Can anyone has code to read a txt file which is in packed decimal (Comp -3) numeric value which was created in main frames system and is 8 characters, but holds a 13 digit number in packed decimal format.

I came across below code

private Decimal Unpack(byte[] inp, int scale)
{
    long lo = 0;
    long mid = 0;
    long hi = 0;
    bool isNegative;

    // this nybble stores only the sign, not a digit.  
    // "C" hex is positive, "D" hex is negative, and "F" hex is unsigned. 
    switch (nibble(inp, 0))
    {
        case 0x0D:
            isNegative = true;
            break;
        case 0x0F:
        case 0x0C:
            isNegative = false;
            break;
        default:
            throw new Exception("Bad sign nibble");
    }
    long intermediate;
    long carry;
    long digit;
    for (int j = inp.Length * 2 - 1; j > 0; j--)
    {
        // multiply by 10
        intermediate = lo * 10;
        lo = intermediate & 0xffffffff;
        carry = intermediate >> 32;
        intermediate = mid * 10 + carry;
        mid = intermediate & 0xffffffff;
        carry = intermediate >> 32;
        intermediate = hi * 10 + carry;
        hi = intermediate & 0xffffffff;
        carry = intermediate >> 32;
        // By limiting input length to 14, we ensure overflow will never occur

        digit = nibble(inp, j);
        if (digit > 9)
        {
            throw new Exception("Bad digit");
        }
        intermediate = lo + digit;
        lo = intermediate & 0xffffffff;
        carry = intermediate >> 32;
        if (carry > 0)
        {
            intermediate = mid + carry;
            mid = intermediate & 0xffffffff;
            carry = intermediate >> 32;
            if (carry > 0)
            {
                intermediate = hi + carry;
                hi = intermediate & 0xffffffff;
                carry = intermediate >> 32;
                // carry should never be non-zero. Back up with validation
            }
        }
    }
    return new Decimal((int)lo, (int)mid, (int)hi, isNegative, (byte)scale);
}

private int nibble(byte[] inp, int nibbleNo)
{
    int b = inp[inp.Length - 1 - nibbleNo / 2];
    return (nibbleNo % 2 == 0) ? (b & 0x0000000F) : (b >> 4);
}

but above code fails saying bad sign nibble.

can anyone confirm if i am reading properly

 using (FileStream fs = new FileStream(pathSource, FileMode.Open))
            {
                using (StreamReader reader = new StreamReader(fs))
                {
                    List<decimal> list = new List<decimal>();

                    while (!reader.EndOfStream)
                    {
                        byte[] b = ASCIIEncoding.ASCII.GetBytes(reader.ReadLine());
                        list.Add(Unpack(b, 0));
                    }

                    reader.Close();
                }
            }

Any help appreciated.

Note: it's not duplicated as I am looking for code that can read a file and pass a parameter to Unpack method.

For reference I added how the data inside the file looks like:

image

c#
.net
comp-3
packed-decimal

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