[WIP] ADPCM decoder

Ryujinx.Audio/ADPCM/Decoder.cs

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+using System;
+
+namespace Ryujinx.Audio.ADPCM
+{
+    class Decoder
+    {
+        private const int SamplesPerFrame = 14;
+
+        private AudioHelper Helper;
+
+        public Decoder()
+        {
+            Helper = new AudioHelper();
+        }
+
+        public short[] Decode(byte[] ADPCM, Info ADPCMInfo, int Samples)
+        {
+            short[] PCM = new short[Samples];
+
+            short   Hist1        = ADPCMInfo.History1;
+            short   Hist2        = ADPCMInfo.History2;
+            short[] Coefficients = ADPCMInfo.Coefficients;
+
+            int FrameCount       = Helper.DivideByRoundUp(Samples, SamplesPerFrame);
+            int SamplesRemaining = Samples;
+
+            int OutIndex = 0;
+            int InIndex  = 0;
+
+            for (int Index = 0; Index < FrameCount; Index++)
+            {
+                byte PredictorScale = ADPCM[InIndex++];
+                int  Scale          = (1 << Helper.GetLowNibble(PredictorScale)) * 2048;
+                int  Predictor      = Helper.GetHighNibble(PredictorScale);
+
+                short Coef1 = ADPCMInfo.Coefficients[Predictor * 2];
+                short Coef2 = ADPCMInfo.Coefficients[Predictor * 2 + 1];
+
+                int SamplesToRead = Math.Min(SamplesPerFrame, SamplesRemaining);
+
+                for (int SampleIndex = 0; SampleIndex < SamplesToRead; SampleIndex++)
+                {
+                    int   ADPCMSample     = SampleIndex % 2 == 0 ? Helper.GetHighNibble(ADPCM[InIndex]) : Helper.GetLowNibble(ADPCM[InIndex++]);
+                    int   Distance        = Scale * ADPCMSample;
+                    int   PredictedSample = Coef1 * Hist1 + Coef2 * Hist2;
+                    int   CorrectedSample = PredictedSample + Distance;
+                    int   ScaledSample    = (CorrectedSample + 1024) >> 11;
+                    short ClampedSample   = Helper.Clamp16(ScaledSample);
+
+                    Hist2 = Hist1;
+                    Hist1 = ClampedSample;
+
+                    PCM[OutIndex++] = ClampedSample;
+                }
+
+                SamplesRemaining -= SamplesToRead;
+            }
+
+            return PCM;
+        }
+    }
+}

Ryujinx.Audio/ADPCM/Info.cs

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+namespace Ryujinx.Audio.ADPCM
+{
+    struct Info
+    {
+        public short   History1;
+        public short   History2;
+        public short[] Coefficients;
+    }
+}

Ryujinx.Audio/AudioHelper.cs

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+using System;
+
+namespace Ryujinx.Audio
+{
+    class AudioHelper
+    {
+        public byte GetHighNibble(byte Value)
+        {
+            return (byte)((Value >> 4) & 0xF);
+        }
+
+        public byte GetLowNibble(byte Value)
+        {
+            return (byte)(Value & 0xF);
+        }
+
+        public short Clamp16(int Value)
+        {
+            if (Value > short.MaxValue)
+                return short.MaxValue;
+            if (Value < short.MinValue)
+                return short.MinValue;
+            return (short)Value;
+        }
+
+        public int DivideByRoundUp(int Value, int Divisor)
+        {
+            return (int)Math.Ceiling((double)Value / Divisor);
+        }
+    }
+}