* Improved BiQuadFilter performance

* Improved implementation for `Vector8`

MonoAudio.Benchmarks/BiQuadBenchmarks.cs

@@ -0,0 +1,48 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+using BenchmarkDotNet.Attributes;
+using BenchmarkDotNet.Jobs;
+
+using MonoAudio.Conversion.Resampling.Sample;
+using MonoAudio.Filters;
+using MonoAudio.Synthesis;
+
+namespace MonoAudio.Benchmarks
+{
+    [SimpleJob(RuntimeMoniker.NetCoreApp50)]
+    public class BiQuadBenchmarks
+    {
+        private IReadableAudioSource<float, SampleFormat> source;
+        private BiQuadFilter filter;
+        private float[] buffer;
+        private const int SampleRate = 192000;
+
+        [Params(1, 2, 3, 4, 8)]
+        public int Channels { get; set; }
+
+        [GlobalSetup]
+        public void Setup()
+        {
+            source = new DummySource<float, SampleFormat>(new SampleFormat(Channels, SampleRate));
+            filter = new BiQuadFilter(source, BiQuadParameter.CreateLPFParameter(SampleRate, 48000, 1));
+            buffer = new float[2560];
+        }
+
+        [Benchmark]
+        public void BiQuadFilter()
+        {
+            var span = buffer.AsSpan();
+            _ = filter.Read(span);
+        }
+
+        [GlobalCleanup]
+        public void Cleanup()
+        {
+            filter?.Dispose();
+            source?.Dispose();
+            buffer = null;
+        }
+    }
+}

MonoAudio.Benchmarks/MonoAudio.Benchmarks.csproj

@@ -1,14 +1,18 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
     <PropertyGroup>
-        <TargetFrameworks>netstandard2.0;net472</TargetFrameworks>
+        <TargetFrameworks>net5.0;netstandard2.0;net472</TargetFrameworks>
+    </PropertyGroup>
+    <PropertyGroup>
+        <PlatformTarget>AnyCPU</PlatformTarget>
+        <DebugType>pdbonly</DebugType>
+        <DebugSymbols>true</DebugSymbols>
     </PropertyGroup>
-
     <ItemGroup>
         <PackageReference Include="BenchmarkDotNet" Version="0.12.1" />
     </ItemGroup>
 
     <ItemGroup>
         <ProjectReference Include="..\MonoAudio\MonoAudio.csproj" />
     </ItemGroup>
-</Project>
+</Project>

MonoAudio.Benchmarks/ResamplerBenchmarks.cs

@@ -10,7 +10,8 @@
 
 namespace MonoAudio.Benchmarks
 {
-    [SimpleJob(RuntimeMoniker.NetCoreApp31)]
+    [SimpleJob(RuntimeMoniker.NetCoreApp50)]
+    [DisassemblyDiagnoser(maxDepth: 16)]
     //[SimpleJob(RuntimeMoniker.Mono, baseline: true)]
     public class ResamplerBenchmarks
     {

MonoAudio/Filters/BiQuadFilter.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Numerics;
+using System.Runtime.CompilerServices;
 using System.Text;
 
 namespace MonoAudio.Filters
@@ -81,24 +82,30 @@ public BiQuadFilter(IReadableAudioSource<float, SampleFormat> source, BiQuadPara
         /// <returns></returns>
         public ReadResult Read(Span<float> buffer)
         {
+            int channels = Format.Channels;
+            buffer = buffer.SliceAlign(channels);
             ReadResult rr = Source.Read(buffer);
             if (rr.HasNoData) return rr;
             var len = rr.Length;
             buffer = buffer.Slice(0, len);
             unsafe
             {
-                for (int i = 0; i < buffer.Length; i += Format.Channels)
+                //Factor localization greatly improved performance
+                Vector3 factorB = Parameter.B;
+                Vector2 factorA = Parameter.A;
+                for (int i = 0; i < buffer.Length; i += channels)
                 {
-                    var span = buffer.Slice(i, internalStates.Length);
+                    ref var pos = ref buffer[i];
+                    //var span = buffer.Slice(i, internalStates.Length);
                     for (int ch = 0; ch < internalStates.Length; ch++)
                     {
                         //Reference: https://en.wikipedia.org/wiki/Digital_biquad_filter#Transposed_Direct_form_2
                         //Transformed for SIMD awareness.
                         ref var a = ref internalStates[ch]; //Persist reference in order to decrease number of times of range check.
-                        ref float v = ref span[ch];
-                        var feedForward = v * Parameter.B; //Multiply in one go
+                        ref float v = ref Unsafe.Add(ref pos, ch);
+                        var feedForward = v * factorB; //Multiply in one go
                         var sum1 = v = feedForward.X + a.X;
-                        var feedBack = sum1 * Parameter.A;  //Multiply in one go
+                        var feedBack = sum1 * factorA;  //Multiply in one go
                         var aY = a.Y;   //Needed backup
                         a = new Vector2(feedForward.Y + feedBack.X + aY, feedForward.Z + feedBack.Y);
                     }