/// <summary>
        /// Base64-encode the given data and return a newly allocated
        /// byte[] with the result.
        /// </summary>
        /// <param name="input">  the data to encode </param>
        /// <param name="offset"> the position within the input array at which to
        ///               start </param>
        /// <param name="len">    the number of bytes of input to encode </param>
        /// <param name="flags">  controls certain features of the encoded output.
        ///               Passing {@code DEFAULT} results in output that
        ///               adheres to RFC 2045. </param>
        public static byte[] encode(byte[] input, int offset, int len, int flags)
        {
            Encoder encoder = new Encoder(flags, null);

            // Compute the exact length of the array we will produce.
            int output_len = len / 3 * 4;

            // Account for the tail of the data and the padding bytes, if any.
            if (encoder.do_padding)
            {
                if (len % 3 > 0)
                {
                    output_len += 4;
                }
            }
            else
            {
                switch (len % 3)
                {
                    case 0:
                        break;
                    case 1:
                        output_len += 2;
                        break;
                    case 2:
                        output_len += 3;
                        break;
                }
            }

            // Account for the newlines, if any.
            if (encoder.do_newline && len > 0)
            {
                output_len += (((len - 1) / (3 * Encoder.LINE_GROUPS)) + 1) * (encoder.do_cr ? 2 : 1);
            }

            encoder.output = new byte[output_len];
            encoder.process(input, offset, len, true);

            Debug.Assert(encoder.op == output_len);

            return encoder.output;
        }