continuity/Benchmarks/MemCasting.cs

// Licensed to Timothy Schenk under the GNU AGPL Version 3 License.

using System.Runtime.InteropServices;
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Order;

namespace Benchmarks;

[Config(typeof(GenericConfig))]
[Orderer(SummaryOrderPolicy.FastestToSlowest)]
public class MemCasting {
    private byte[] _data = null!;
    private byte[] _arrayData = null!;

    [Params(1000, 100000, 1000000)] public int N;
    [GlobalSetup]
    public void Setup() {
        _data = new byte[64];
        _arrayData = new byte[N * 64];
        Random.Shared.NextBytes(_data);
        Random.Shared.NextBytes(_arrayData);
    }
    private static ElementalStats ReadElementalStatsMemoryMarshal(ref Span<byte> data) {
        return MemoryMarshal.Cast<byte, ElementalStats>(data.Slice(0, 64))[0];
    }
    private static ElementalStats ReadElementalStatsMemoryMarshal2(ref Span<byte> data) {
        return MemoryMarshal.Read<ElementalStats>(data.Slice(0, 64));
    }
    private static ElementalStats ReadElementalStatsNew(ref Span<byte> data) {
        return new ElementalStats {
            MinimumFireDamage = BitConverter.ToInt32(data.Slice(0, 4)), // 140 -> 144
            MinimumWaterDamage = BitConverter.ToInt32(data.Slice(4, 4)), // 144 -> 148
            MinimumDarkDamage = BitConverter.ToInt32(data.Slice(8, 4)), // 148 -> 152
            MinimumHolyDamage = BitConverter.ToInt32(data.Slice(12, 4)), // 152 -> 156
            MaximumFireDamage = BitConverter.ToInt32(data.Slice(16, 4)), // 156 -> 160
            MaximumWaterDamage = BitConverter.ToInt32(data.Slice(20, 4)), // 160 -> 164
            MaximumDarkDamage = BitConverter.ToInt32(data.Slice(24, 4)), // 164 -> 168
            MaximumHolyDamage = BitConverter.ToInt32(data.Slice(28, 4)), // 168 -> 172
            ElementFire = BitConverter.ToUInt32(data.Slice(32, 4)), // 172 -> 176
            ElementWater = BitConverter.ToUInt32(data.Slice(36, 4)), // 176 -> 180
            ElementDark = BitConverter.ToUInt32(data.Slice(40, 4)), // 180 -> 184
            ElementHoly = BitConverter.ToUInt32(data.Slice(44, 4)), // 184 -> 188
            FireResistance = BitConverter.ToInt32(data.Slice(48, 4)), // 188 -> 192
            WaterResistance = BitConverter.ToInt32(data.Slice(52, 4)), // 192 -> 196
            DarkResistance = BitConverter.ToInt32(data.Slice(56, 4)), // 196 -> 200
            HolyResistance = BitConverter.ToInt32(data.Slice(60, 4)) // 200 -> 204
        };
    }

    [Benchmark]
    public Span<ElementalStats> MemoryMarshalCastArray() {
        var data = _arrayData.AsSpan();
        var elements = MemoryMarshal.Cast<byte, ElementalStats>(data);

        return elements;
    }

    [Benchmark]
    public Span<ElementalStats> MemoryMarshalReadArray() {
        Span<ElementalStats> statsArr = stackalloc ElementalStats[N + 1];
        var data = _data.AsSpan();
        for (int i = 0; i <= N; i++) {
            statsArr[i] = ReadElementalStatsMemoryMarshal2(ref data);
        }

        return statsArr.ToArray();
    }
    [Benchmark]
    public Span<ElementalStats> ManualSpanSlicingArray() {
        Span<ElementalStats> statsArr = stackalloc ElementalStats[N + 1];
        var data = _data.AsSpan();
        for (int i = 0; i <= N; i++) {
            statsArr[i] = ReadElementalStatsNew(ref data);
        }

        return statsArr.ToArray();
    }

    [Benchmark]
    public ElementalStats MemoryMarshalCastSingle() {
        var data = _data.AsSpan();
        return ReadElementalStatsMemoryMarshal(ref data);
    }

    [Benchmark]
    public ElementalStats MemoryMarshalReadSingle() {
        var data = _data.AsSpan();
        return ReadElementalStatsMemoryMarshal2(ref data);
    }
    [Benchmark]
    public ElementalStats ManualSpanSlicingSingle() {
        var data = _data.AsSpan();
        return ReadElementalStatsNew(ref data);
    }

    [StructLayout(LayoutKind.Explicit, Size = 64)]
    public struct ElementalStats {
        [FieldOffset(0)]
        [MarshalAs(UnmanagedType.I4)]
        public int MinimumFireDamage;

        [FieldOffset(4)]
        [MarshalAs(UnmanagedType.I4)]
        public int MinimumWaterDamage;

        [FieldOffset(8)]
        [MarshalAs(UnmanagedType.I4)]
        public int MinimumDarkDamage;

        [FieldOffset(12)]
        [MarshalAs(UnmanagedType.I4)]
        public int MinimumHolyDamage;

        [FieldOffset(16)]
        [MarshalAs(UnmanagedType.I4)]
        public int MaximumFireDamage;

        [FieldOffset(20)]
        [MarshalAs(UnmanagedType.I4)]
        public int MaximumWaterDamage;

        [FieldOffset(24)]
        [MarshalAs(UnmanagedType.I4)]
        public int MaximumDarkDamage;

        [FieldOffset(28)]
        [MarshalAs(UnmanagedType.I4)]
        public int MaximumHolyDamage;

        [FieldOffset(32)]
        [MarshalAs(UnmanagedType.U4)]
        public uint ElementFire;

        [FieldOffset(36)]
        [MarshalAs(UnmanagedType.U4)]
        public uint ElementWater;

        [FieldOffset(40)]
        [MarshalAs(UnmanagedType.U4)]
        public uint ElementDark;

        [FieldOffset(44)]
        [MarshalAs(UnmanagedType.U4)]
        public uint ElementHoly;

        [FieldOffset(48)]
        [MarshalAs(UnmanagedType.I4)]
        public int FireResistance;

        [FieldOffset(52)]
        [MarshalAs(UnmanagedType.I4)]
        public int WaterResistance;

        [FieldOffset(56)]
        [MarshalAs(UnmanagedType.I4)]
        public int DarkResistance;

        [FieldOffset(60)]
        [MarshalAs(UnmanagedType.I4)]
        public int HolyResistance;
    }

}