コード例 #1
0
ファイル: Header.cs プロジェクト: roxya/ClassicUO
        /// <summary>
        ///     Read a 32-bit header from the bitstream.
        /// </summary>
        internal void read_header(Bitstream stream, Crc16[] crcp)
        {
            int headerstring;
            int channel_bitrate;

            bool sync = false;

            do
            {
                headerstring   = stream.syncHeader(syncmode);
                h_headerstring = headerstring; // E.B

                if (syncmode == Bitstream.INITIAL_SYNC)
                {
                    h_version = ((SupportClass.URShift(headerstring, 19)) & 1);
                    if (((SupportClass.URShift(headerstring, 20)) & 1) == 0)
                    {
                        // SZD: MPEG2.5 detection
                        if (h_version == MPEG2_LSF)
                        {
                            h_version = MPEG25_LSF;
                        }
                        else
                        {
                            throw stream.newBitstreamException(BitstreamErrors.UNKNOWN_ERROR);
                        }
                    }

                    if ((h_sample_frequency = ((SupportClass.URShift(headerstring, 10)) & 3)) == 3)
                    {
                        throw stream.newBitstreamException(BitstreamErrors.UNKNOWN_ERROR);
                    }
                }

                h_layer          = 4 - (SupportClass.URShift(headerstring, 17)) & 3;
                h_protection_bit = (SupportClass.URShift(headerstring, 16)) & 1;
                h_bitrate_index  = (SupportClass.URShift(headerstring, 12)) & 0xF;
                h_padding_bit    = (SupportClass.URShift(headerstring, 9)) & 1;
                h_mode           = ((SupportClass.URShift(headerstring, 6)) & 3);
                h_mode_extension = (SupportClass.URShift(headerstring, 4)) & 3;
                if (h_mode == JOINT_STEREO)
                {
                    h_intensity_stereo_bound = (h_mode_extension << 2) + 4;
                }
                else
                {
                    h_intensity_stereo_bound = 0;
                }
                // should never be used
                if (((SupportClass.URShift(headerstring, 3)) & 1) == 1)
                {
                    h_copyright = true;
                }
                if (((SupportClass.URShift(headerstring, 2)) & 1) == 1)
                {
                    h_original = true;
                }

                // calculate number of subbands:
                if (h_layer == 1)
                {
                    h_number_of_subbands = 32;
                }
                else
                {
                    channel_bitrate = h_bitrate_index;
                    // calculate bitrate per channel:
                    if (h_mode != SINGLE_CHANNEL)
                    {
                        if (channel_bitrate == 4)
                        {
                            channel_bitrate = 1;
                        }
                        else
                        {
                            channel_bitrate -= 4;
                        }
                    }

                    if ((channel_bitrate == 1) || (channel_bitrate == 2))
                    {
                        if (h_sample_frequency == THIRTYTWO)
                        {
                            h_number_of_subbands = 12;
                        }
                        else
                        {
                            h_number_of_subbands = 8;
                        }
                    }
                    else if ((h_sample_frequency == FOURTYEIGHT) || ((channel_bitrate >= 3) && (channel_bitrate <= 5)))
                    {
                        h_number_of_subbands = 27;
                    }
                    else
                    {
                        h_number_of_subbands = 30;
                    }
                }
                if (h_intensity_stereo_bound > h_number_of_subbands)
                {
                    h_intensity_stereo_bound = h_number_of_subbands;
                }
                // calculate framesize and nSlots
                calculate_framesize();

                // read framedata:
                stream.read_frame_data(framesize);

                if (stream.IsSyncCurrentPosition(syncmode))
                {
                    if (syncmode == Bitstream.INITIAL_SYNC)
                    {
                        syncmode = Bitstream.STRICT_SYNC;
                        stream.SetSyncWord(headerstring & unchecked ((int)0xFFF80CC0));
                    }
                    sync = true;
                }
                else
                {
                    stream.unreadFrame();
                }
            } while (!sync);

            stream.ParseFrame();

            if (h_protection_bit == 0)
            {
                // frame contains a crc checksum
                checksum = (short)stream.GetBitsFromBuffer(16);
                if (crc == null)
                {
                    crc = new Crc16();
                }
                crc.add_bits(headerstring, 16);
                crcp[0] = crc;
            }
            else
            {
                crcp[0] = null;
            }
            if (h_sample_frequency == FOURTYFOUR_POINT_ONE)
            {
                /*
                 * if (offset == null)
                 * {
                 * int max = max_number_of_frames(stream);
                 * offset = new int[max];
                 * for(int i=0; i<max; i++) offset[i] = 0;
                 * }
                 * // Bizarre, y avait ici une acollade ouvrante
                 * int cf = stream.current_frame();
                 * int lf = stream.last_frame();
                 * if ((cf > 0) && (cf == lf))
                 * {
                 * offset[cf] = offset[cf-1] + h_padding_bit;
                 * }
                 * else
                 * {
                 * offset[0] = h_padding_bit;
                 * }
                 */
            }
        }