十六进制也字节数组转换问题,我想知道原理是怎么样的

        public static byte[] HexStringToByteArray(string s)
        {
            Byte[] buf = new byte[s.Length / 2];
            for (int i = 0; i < buf.Length; i++)
            {
                buf[i] = (byte)(chr2hex(s.Substring(i * 2, 1)) * 0x10 + chr2hex(s.Substring(i * 2 + 1, 1)));
            }            return buf;
        }
        private static byte chr2hex(string chr)
        {
            switch (chr)
            {
                case "0":
                    return 0x00;
                case "1":
                    return 0x01;
                case "2":
                    return 0x02;
                case "3":
                    return 0x03;
                case "4":
                    return 0x04;
                case "5":
                    return 0x05;
                case "6":
                    return 0x06;
                case "7":
                    return 0x07;
                case "8":
                    return 0x08;
                case "9":
                    return 0x09;
                case "A":
                    return 0x0a;
                case "B":
                    return 0x0b;
                case "C":
                    return 0x0c;
                case "D":
                    return 0x0d;
                case "E":
                    return 0x0e;
                case "F":
                    return 0x0f;
            }
            return 0x00;
        } buf[i] = (byte)(chr2hex(s.Substring(i * 2, 1)) * 0x10 + chr2hex(s.Substring(i * 2 + 1, 1)));
不明白这句话是什么意思,谁能解释一下越通俗越好,谢谢