HwOpus service implementation (#201)

* Started to implement the hwopus service

* Write outputs on decode method, some basic error handling

* Fix buffer size read from header and check

* Fix order of values

Ryujinx.HLE/HOS/Services/Aud/IHardwareOpusDecoder.cs

@@ -0,0 +1,91 @@
+using Concentus.Structs;
+using Ryujinx.HLE.HOS.Ipc;
+using System.Collections.Generic;
+
+using static Ryujinx.HLE.HOS.ErrorCode;
+
+namespace Ryujinx.HLE.HOS.Services.Aud
+{
+    class IHardwareOpusDecoder : IpcService
+    {
+        private const int FixedSampleRate = 48000;
+
+        private Dictionary<int, ServiceProcessRequest> m_Commands;
+
+        public override IReadOnlyDictionary<int, ServiceProcessRequest> Commands => m_Commands;
+
+        private int SampleRate;
+        private int ChannelsCount;
+
+        private OpusDecoder Decoder;
+
+        public IHardwareOpusDecoder(int SampleRate, int ChannelsCount)
+        {
+            m_Commands = new Dictionary<int, ServiceProcessRequest>()
+            {
+                { 0, DecodeInterleaved         },
+                { 4, DecodeInterleavedWithPerf }
+            };
+
+            this.SampleRate    = SampleRate;
+            this.ChannelsCount = ChannelsCount;
+
+            Decoder = new OpusDecoder(FixedSampleRate, ChannelsCount);
+        }
+
+        public long DecodeInterleavedWithPerf(ServiceCtx Context)
+        {
+            long Result = DecodeInterleaved(Context);
+
+            //TODO: Figure out what this value is.
+            //According to switchbrew, it is now used.
+            Context.ResponseData.Write(0L);
+
+            return Result;
+        }
+
+        public long DecodeInterleaved(ServiceCtx Context)
+        {
+            long InPosition = Context.Request.SendBuff[0].Position;
+            long InSize     = Context.Request.SendBuff[0].Size;
+
+            if (InSize < 8)
+            {
+                return MakeError(ErrorModule.Audio, AudErr.OpusInvalidInput);
+            }
+
+            long OutPosition = Context.Request.ReceiveBuff[0].Position;
+            long OutSize     = Context.Request.ReceiveBuff[0].Size;
+
+            byte[] OpusData = Context.Memory.ReadBytes(InPosition, InSize);
+
+            int Processed = ((OpusData[0] << 24) |
+                             (OpusData[1] << 16) |
+                             (OpusData[2] << 8)  |
+                             (OpusData[3] << 0)) + 8;
+
+            if ((uint)Processed > (ulong)InSize)
+            {
+                return MakeError(ErrorModule.Audio, AudErr.OpusInvalidInput);
+            }
+
+            short[] Pcm = new short[OutSize / 2];
+
+            int FrameSize = Pcm.Length / (ChannelsCount * 2);
+
+            int Samples = Decoder.Decode(OpusData, 0, OpusData.Length, Pcm, 0, FrameSize);
+
+            foreach (short Sample in Pcm)
+            {
+                Context.Memory.WriteInt16(OutPosition, Sample);
+
+                OutPosition += 2;
+            }
+
+            Context.ResponseData.Write(Processed);
+            Context.ResponseData.Write(Samples);
+
+            return 0;
+        }
+    }
+}