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using System;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
namespace Ryujinx.Audio.Backends.CompatLayer
{
public static class Downmixing
{
[StructLayout(LayoutKind.Sequential, Pack = 1)]
private struct Channel51FormatPCM16
{
public short FrontLeft;
public short FrontRight;
public short FrontCenter;
public short LowFrequency;
public short BackLeft;
public short BackRight;
}
[StructLayout(LayoutKind.Sequential, Pack = 1)]
private struct ChannelStereoFormatPCM16
{
public short Left;
public short Right;
}
private const int Q15Bits = 16;
private const int RawQ15One = 1 << Q15Bits;
private const int RawQ15HalfOne = (int)(0.5f * RawQ15One);
private const int Minus3dBInQ15 = (int)(0.707f * RawQ15One);
private const int Minus6dBInQ15 = (int)(0.501f * RawQ15One);
private const int Minus12dBInQ15 = (int)(0.251f * RawQ15One);
private static readonly int[] DefaultSurroundToStereoCoefficients = new int[4]
{
RawQ15One,
Minus3dBInQ15,
Minus12dBInQ15,
Minus3dBInQ15
};
private static readonly int[] DefaultStereoToMonoCoefficients = new int[2]
{
Minus6dBInQ15,
Minus6dBInQ15
};
private const int SurroundChannelCount = 6;
private const int StereoChannelCount = 2;
private const int MonoChannelCount = 1;
[MethodImpl(MethodImplOptions.AggressiveInlining)]
private static ReadOnlySpan<Channel51FormatPCM16> GetSurroundBuffer(ReadOnlySpan<short> data)
{
return MemoryMarshal.Cast<short, Channel51FormatPCM16>(data);
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
private static ReadOnlySpan<ChannelStereoFormatPCM16> GetStereoBuffer(ReadOnlySpan<short> data)
{
return MemoryMarshal.Cast<short, ChannelStereoFormatPCM16>(data);
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
private static short DownMixStereoToMono(ReadOnlySpan<int> coefficients, short left, short right)
{
return (short)((left * coefficients[0] + right * coefficients[1]) >> Q15Bits);
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
private static short DownMixSurroundToStereo(ReadOnlySpan<int> coefficients, short back, short lfe, short center, short front)
{
return (short)((coefficients[3] * back + coefficients[2] * lfe + coefficients[1] * center + coefficients[0] * front + RawQ15HalfOne) >> Q15Bits);
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
private static short[] DownMixSurroundToStereo(ReadOnlySpan<int> coefficients, ReadOnlySpan<short> data)
{
int samplePerChannelCount = data.Length / SurroundChannelCount;
short[] downmixedBuffer = new short[samplePerChannelCount * StereoChannelCount];
ReadOnlySpan<Channel51FormatPCM16> channels = GetSurroundBuffer(data);
for (int i = 0; i < samplePerChannelCount; i++)
{
Channel51FormatPCM16 channel = channels[i];
downmixedBuffer[i * 2] = DownMixSurroundToStereo(coefficients, channel.BackLeft, channel.LowFrequency, channel.FrontCenter, channel.FrontLeft);
downmixedBuffer[i * 2 + 1] = DownMixSurroundToStereo(coefficients, channel.BackRight, channel.LowFrequency, channel.FrontCenter, channel.FrontRight);
}
return downmixedBuffer;
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
private static short[] DownMixStereoToMono(ReadOnlySpan<int> coefficients, ReadOnlySpan<short> data)
{
int samplePerChannelCount = data.Length / StereoChannelCount;
short[] downmixedBuffer = new short[samplePerChannelCount * MonoChannelCount];
ReadOnlySpan<ChannelStereoFormatPCM16> channels = GetStereoBuffer(data);
for (int i = 0; i < samplePerChannelCount; i++)
{
ChannelStereoFormatPCM16 channel = channels[i];
downmixedBuffer[i] = DownMixStereoToMono(coefficients, channel.Left, channel.Right);
}
return downmixedBuffer;
}
public static short[] DownMixStereoToMono(ReadOnlySpan<short> data)
{
return DownMixStereoToMono(DefaultStereoToMonoCoefficients, data);
}
public static short[] DownMixSurroundToStereo(ReadOnlySpan<short> data)
{
return DownMixSurroundToStereo(DefaultSurroundToStereoCoefficients, data);
}
}
}
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