Bio.IO.BAM.BAMFormatter.GetEncodedSequence C# (CSharp) Method

        private static byte[] GetEncodedSequence(SAMAlignedSequence alignedSeq)
        {
            List<byte> byteList = new List<byte>();
            ISequence seq = alignedSeq.QuerySequence;
            if (seq != null)
            {
                if (!(seq.Alphabet is DnaAlphabet))
                {
                    throw new ArgumentException(Properties.Resource.BAMFormatterSupportsDNAOnly);
                }

                byte[] symbolMap = seq.Alphabet.GetSymbolValueMap();

                for (int i = 0; i < seq.Count; i++)
                {
                    char symbol = (char)symbolMap[seq[i]];
                    byte encodedvalue = 0;

                  
                    // 4-bit encoded read: =ACMGRSVTWYHKDBN -> 0-15; the earlier base is stored in the 
                    // high-order 4 bits of the byte.
                    //Note:
                    // All the other symbols which are not supported by BAM specification (other than "=ACMGRSVTWYHKDBN") are converted to 'N'
                    // for example a '.' symbol which is supported by SAM specification will be converted to symbol 'N'
                    switch (symbol)
                    {
                        case '=':
                            encodedvalue = 0;
                            break;
                        case 'A':
                            encodedvalue = 1;
                            break;
                        case 'C':
                            encodedvalue = 2;
                            break;
                        case 'M':
                            encodedvalue = 3;
                            break;
                        case 'G':
                            encodedvalue = 4;
                            break;
                        case 'R':
                            encodedvalue = 5;
                            break;
                        case 'S':
                            encodedvalue = 6;
                            break;
                        case 'V':
                            encodedvalue = 7;
                            break;
                        case 'T':
                            encodedvalue = 8;
                            break;
                        case 'W':
                            encodedvalue = 9;
                            break;
                        case 'Y':
                            encodedvalue = 10;
                            break;
                        case 'H':
                            encodedvalue = 11;
                            break;
                        case 'K':
                            encodedvalue = 12;
                            break;
                        case 'D':
                            encodedvalue = 13;
                            break;
                        case 'B':
                            encodedvalue = 14;
                            break;
                        default:
                            encodedvalue = 15;
                            break;
                    }

                    if ((i + 1) % 2 > 0)
                    {
                        byteList.Add((byte)(encodedvalue << 4));
                    }
                    else
                    {
                        byteList[byteList.Count - 1] = (byte)(byteList[byteList.Count - 1] | encodedvalue);
                    }
                }
            }

            return byteList.ToArray();
        }