Add a benchmark to test C#s ability to reduce modulus

Author: Genbox

Src/FastData.Benchmarks/Benchmarks/FastModBenchmarks.cs

@@ -0,0 +1,44 @@
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using System.Runtime.Intrinsics.X86;
+using Genbox.FastData.Generators.Helpers;
+
+namespace Genbox.FastData.Benchmarks.Benchmarks;
+
+/// <summary>Benchmarks the difference between normal modulus and FastMod</summary>
+public class FastModBenchmarks
+{
+    private readonly uint _value = 3_000_000_000; //Note: Do not make this const!
+    private readonly ushort _mod = 1024; //Note: Do not make this const!
+    private const ushort _modConst = 1024;
+
+    private readonly ulong _mult = MathHelper.GetFastModMultiplier(int.MaxValue);
+    private readonly uint _mult2 = GetFastModMultiplierSmall(3000);
+
+    [Benchmark]
+    public uint Const() => _value % 1024;
+
+    [Benchmark]
+    public uint ConstAdd() => _value & 1023;
+
+    [Benchmark]
+    public long Var() => _value % _mod;
+
+    [Benchmark]
+    public long VarConst() => _value % _modConst;
+
+    [Benchmark]
+    public long VarAdd() => _value & 1023;
+
+    [Benchmark]
+    public ulong FastMod() => MathHelper.FastMod(_value, 1024, _mult);
+
+    [Benchmark]
+    public ulong FastModSmall() => FastModSmall(3000, 1024, _mult2);
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private static uint GetFastModMultiplierSmall(uint divisor) => unchecked((uint.MaxValue / divisor) + 1);
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private static ulong FastModSmall(ushort value, ushort divisor, uint multiplier) => ((ulong)(multiplier * value) * divisor) >> 32;
+}