Add C# project

CSharp/LibAtrac9.sln

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+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio 15
+VisualStudioVersion = 15.0.27130.2003
+MinimumVisualStudioVersion = 15.0.26124.0
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "LibAtrac9", "LibAtrac9\LibAtrac9.csproj", "{2414DAA9-779C-4E7E-A97F-4DE09B22B88F}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Debug|ARM = Debug|ARM
+		Debug|x64 = Debug|x64
+		Debug|x86 = Debug|x86
+		Release|Any CPU = Release|Any CPU
+		Release|ARM = Release|ARM
+		Release|x64 = Release|x64
+		Release|x86 = Release|x86
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{2414DAA9-779C-4E7E-A97F-4DE09B22B88F}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{2414DAA9-779C-4E7E-A97F-4DE09B22B88F}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{2414DAA9-779C-4E7E-A97F-4DE09B22B88F}.Debug|ARM.ActiveCfg = Debug|Any CPU
+		{2414DAA9-779C-4E7E-A97F-4DE09B22B88F}.Debug|ARM.Build.0 = Debug|Any CPU
+		{2414DAA9-779C-4E7E-A97F-4DE09B22B88F}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{2414DAA9-779C-4E7E-A97F-4DE09B22B88F}.Debug|x64.Build.0 = Debug|Any CPU
+		{2414DAA9-779C-4E7E-A97F-4DE09B22B88F}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{2414DAA9-779C-4E7E-A97F-4DE09B22B88F}.Debug|x86.Build.0 = Debug|Any CPU
+		{2414DAA9-779C-4E7E-A97F-4DE09B22B88F}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{2414DAA9-779C-4E7E-A97F-4DE09B22B88F}.Release|Any CPU.Build.0 = Release|Any CPU
+		{2414DAA9-779C-4E7E-A97F-4DE09B22B88F}.Release|ARM.ActiveCfg = Release|Any CPU
+		{2414DAA9-779C-4E7E-A97F-4DE09B22B88F}.Release|ARM.Build.0 = Release|Any CPU
+		{2414DAA9-779C-4E7E-A97F-4DE09B22B88F}.Release|x64.ActiveCfg = Release|Any CPU
+		{2414DAA9-779C-4E7E-A97F-4DE09B22B88F}.Release|x64.Build.0 = Release|Any CPU
+		{2414DAA9-779C-4E7E-A97F-4DE09B22B88F}.Release|x86.ActiveCfg = Release|Any CPU
+		{2414DAA9-779C-4E7E-A97F-4DE09B22B88F}.Release|x86.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {2AFD09F0-D995-47ED-AA86-FFA93824A514}
+	EndGlobalSection
+EndGlobal

CSharp/LibAtrac9/Atrac9Config.cs

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+using System.IO;
+using LibAtrac9.Utilities;
+
+namespace LibAtrac9
+{
+    /// <summary>
+    /// Stores the configuration data needed to decode or encode an ATRAC9 stream.
+    /// </summary>
+    public class Atrac9Config
+    {
+        /// <summary>
+        /// The 4-byte ATRAC9 configuration data.
+        /// </summary>
+        public byte[] ConfigData { get; }
+
+        /// <summary>
+        /// A 4-bit value specifying one of 16 sample rates.
+        /// </summary>
+        public int SampleRateIndex { get; }
+        /// <summary>
+        /// A 3-bit value specifying one of 6 substream channel mappings.
+        /// </summary>
+        public int ChannelConfigIndex { get; }
+        /// <summary>
+        /// An 11-bit value containing the average size of a single frame.
+        /// </summary>
+        public int FrameBytes { get; }
+        /// <summary>
+        /// A 2-bit value indicating how many frames are in each superframe.
+        /// </summary>
+        public int SuperframeIndex { get; }
+
+        /// <summary>
+        /// The channel mapping used by the ATRAC9 stream.
+        /// </summary>
+        public ChannelConfig ChannelConfig { get; }
+        /// <summary>
+        /// The total number of channels in the ATRAC9 stream.
+        /// </summary>
+        public int ChannelCount { get; }
+        /// <summary>
+        /// The sample rate of the ATRAC9 stream.
+        /// </summary>
+        public int SampleRate { get; }
+        /// <summary>
+        /// Indicates whether the ATRAC9 stream has a <see cref="SampleRateIndex"/> of 8 or above.
+        /// </summary>
+        public bool HighSampleRate { get; }
+
+        /// <summary>
+        /// The number of frames in each superframe.
+        /// </summary>
+        public int FramesPerSuperframe { get; }
+        /// <summary>
+        /// The number of samples in one frame as an exponent of 2.
+        /// <see cref="FrameSamples"/> = 2^<see cref="FrameSamplesPower"/>.
+        /// </summary>
+        public int FrameSamplesPower { get; }
+        /// <summary>
+        /// The number of samples in one frame.
+        /// </summary>
+        public int FrameSamples { get; }
+        /// <summary>
+        /// The number of bytes in one superframe.
+        /// </summary>
+        public int SuperframeBytes { get; }
+        /// <summary>
+        /// The number of samples in one superframe.
+        /// </summary>
+        public int SuperframeSamples { get; }
+
+        /// <summary>
+        /// Reads ATRAC9 configuration data and calculates the stream parameters from it.
+        /// </summary>
+        /// <param name="configData">The processed ATRAC9 configuration.</param>
+        public Atrac9Config(byte[] configData)
+        {
+            if (configData == null || configData.Length != 4)
+            {
+                throw new InvalidDataException("Config data must be 4 bytes long");
+            }
+
+            ReadConfigData(configData, out int a, out int b, out int c, out int d);
+            SampleRateIndex = a;
+            ChannelConfigIndex = b;
+            FrameBytes = c;
+            SuperframeIndex = d;
+            ConfigData = configData;
+
+            FramesPerSuperframe = 1 << SuperframeIndex;
+            SuperframeBytes = FrameBytes << SuperframeIndex;
+            ChannelConfig = Tables.ChannelConfig[ChannelConfigIndex];
+
+            ChannelCount = ChannelConfig.ChannelCount;
+            SampleRate = Tables.SampleRates[SampleRateIndex];
+            HighSampleRate = SampleRateIndex > 7;
+            FrameSamplesPower = Tables.SamplingRateIndexToFrameSamplesPower[SampleRateIndex];
+            FrameSamples = 1 << FrameSamplesPower;
+            SuperframeSamples = FrameSamples * FramesPerSuperframe;
+        }
+
+        private static void ReadConfigData(byte[] configData, out int sampleRateIndex, out int channelConfigIndex, out int frameBytes, out int superframeIndex)
+        {
+            var reader = new BitReader(configData);
+
+            int header = reader.ReadInt(8);
+            sampleRateIndex = reader.ReadInt(4);
+            channelConfigIndex = reader.ReadInt(3);
+            int validationBit = reader.ReadInt(1);
+            frameBytes = reader.ReadInt(11) + 1;
+            superframeIndex = reader.ReadInt(2);
+
+            if (header != 0xFE || validationBit != 0)
+            {
+                throw new InvalidDataException("ATRAC9 Config Data is invalid");
+            }
+        }
+    }
+}

CSharp/LibAtrac9/Atrac9Decoder.cs

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+using System;
+using LibAtrac9.Utilities;
+
+namespace LibAtrac9
+{
+    /// <summary>
+    /// Decodes an ATRAC9 stream into 16-bit PCM.
+    /// </summary>
+    public class Atrac9Decoder
+    {
+        /// <summary>
+        /// The config data for the current ATRAC9 stream.
+        /// </summary>
+        public Atrac9Config Config { get; private set; }
+
+        private Frame Frame { get; set; }
+        private BitReader Reader { get; set; }
+        private bool _initialized;
+
+        /// <summary>
+        /// Sets up the decoder to decode an ATRAC9 stream based on the information in <paramref name="configData"/>.
+        /// </summary>
+        /// <param name="configData">A 4-byte value containing information about the ATRAC9 stream.</param>
+        public void Initialize(byte[] configData)
+        {
+            Config = new Atrac9Config(configData);
+            Frame = new Frame(Config);
+            Reader = new BitReader(null);
+            _initialized = true;
+        }
+
+        /// <summary>
+        /// Decodes one superframe of ATRAC9 data.
+        /// </summary>
+        /// <param name="atrac9Data">The ATRAC9 data to decode. The array must be at least
+        /// <see cref="Config"/>.<see cref="Atrac9Config.SuperframeBytes"/> bytes long.</param>
+        /// <param name="pcmOut">A buffer that the decoded PCM data will be placed in.
+        /// The array must have dimensions of at least [<see cref="Config"/>.<see cref="Atrac9Config.ChannelCount"/>]
+        /// [<see cref="Config"/>.<see cref="Atrac9Config.SuperframeSamples"/>].</param>
+        public void Decode(byte[] atrac9Data, short[][] pcmOut)
+        {
+            if (!_initialized) throw new InvalidOperationException("Decoder must be initialized before decoding.");
+
+            ValidateDecodeBuffers(atrac9Data, pcmOut);
+            Reader.SetBuffer(atrac9Data);
+            DecodeSuperFrame(pcmOut);
+        }
+
+        private void ValidateDecodeBuffers(byte[] atrac9Buffer, short[][] pcmBuffer)
+        {
+            if (atrac9Buffer == null) throw new ArgumentNullException(nameof(atrac9Buffer));
+            if (pcmBuffer == null) throw new ArgumentNullException(nameof(pcmBuffer));
+
+            if (atrac9Buffer.Length < Config.SuperframeBytes)
+            {
+                throw new ArgumentException("ATRAC9 buffer is too small");
+            }
+
+            if (pcmBuffer.Length < Config.ChannelCount)
+            {
+                throw new ArgumentException("PCM buffer is too small");
+            }
+
+            for (int i = 0; i < Config.ChannelCount; i++)
+            {
+                if (pcmBuffer[i]?.Length < Config.SuperframeSamples)
+                {
+                    throw new ArgumentException("PCM buffer is too small");
+                }
+            }
+        }
+
+        private void DecodeSuperFrame(short[][] pcmOut)
+        {
+            for (int i = 0; i < Config.FramesPerSuperframe; i++)
+            {
+                Frame.FrameIndex = i;
+                DecodeFrame(Reader, Frame);
+                PcmFloatToShort(pcmOut, i * Config.FrameSamples);
+                Reader.AlignPosition(8);
+            }
+        }
+
+        private void PcmFloatToShort(short[][] pcmOut, int start)
+        {
+            int endSample = start + Config.FrameSamples;
+            int channelNum = 0;
+            foreach (Block block in Frame.Blocks)
+            {
+                foreach (Channel channel in block.Channels)
+                {
+                    double[] pcmSrc = channel.Pcm;
+                    short[] pcmDest = pcmOut[channelNum++];
+                    for (int d = 0, s = start; s < endSample; d++, s++)
+                    {
+                        double sample = pcmSrc[d];
+                        // Not using Math.Round because it's ~20x slower on 64-bit
+                        int roundedSample = (int)Math.Floor(sample + 0.5);
+                        pcmDest[s] = Helpers.Clamp16(roundedSample);
+                    }
+                }
+            }
+        }
+
+        private static void DecodeFrame(BitReader reader, Frame frame)
+        {
+            Unpack.UnpackFrame(reader, frame);
+
+            foreach (Block block in frame.Blocks)
+            {
+                Quantization.DequantizeSpectra(block);
+                Stereo.ApplyIntensityStereo(block);
+                Quantization.ScaleSpectrum(block);
+                BandExtension.ApplyBandExtension(block);
+                ImdctBlock(block);
+            }
+        }
+
+        private static void ImdctBlock(Block block)
+        {
+            foreach (Channel channel in block.Channels)
+            {
+                channel.Mdct.RunImdct(channel.Spectra, channel.Pcm);
+            }
+        }
+    }
+}

CSharp/LibAtrac9/Atrac9Rng.cs

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+namespace LibAtrac9
+{
+    /// <summary>
+    /// An Xorshift RNG used by the ATRAC9 codec
+    /// </summary>
+    internal class Atrac9Rng
+    {
+        private ushort _stateA;
+        private ushort _stateB;
+        private ushort _stateC;
+        private ushort _stateD;
+
+        public Atrac9Rng(ushort seed)
+        {
+            int startValue = 0x4D93 * (seed ^ (seed >> 14));
+
+            _stateA = (ushort)(3 - startValue);
+            _stateB = (ushort)(2 - startValue);
+            _stateC = (ushort)(1 - startValue);
+            _stateD = (ushort)(0 - startValue);
+        }
+
+        public ushort Next()
+        {
+            ushort t = (ushort)(_stateD ^ (_stateD << 5));
+            _stateD = _stateC;
+            _stateC = _stateB;
+            _stateB = _stateA;
+            _stateA = (ushort)(t ^ _stateA ^ ((t ^ (_stateA >> 5)) >> 4));
+            return _stateA;
+        }
+    }
+}