CSharp_PartitaIva_CheckSum_Algorithm

static readonly byte[] _oddMap = new byte[] { 0, 2, 4, 6, 8, 1, 3, 5, 7, 9 };
static bool PartitaIvaCheckSum(string value)
{
    Debug.Assert(value is not null);
    Debug.Assert(value.Length == 11);
    // ASSERT: value is a string of digits
    
    var c0 = (byte) '0';
    int acc = 0;
    byte[] codes = Encoding.ASCII.GetBytes(value);
    for (var pos = 0; pos < 11; ++pos)
    {
        var ci = codes[pos] - c0;
        if (pos % 2 == 0) acc += ci;
        else acc += _oddMap[ci];
    }

    return acc % 10 == 0;
}