https://habr.com/ru/post/722368/

# Array For Benchmarks.md

Array for/foreach benchmarks

ArrayReadBenchmark.cs

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Jobs;
using System.Runtime.InteropServices;
using System.Runtime.CompilerServices;

namespace Storage.Benchmark;

[SimpleJob(RuntimeMoniker.Net80)]
[SimpleJob(RuntimeMoniker.Net70)]
[SimpleJob(RuntimeMoniker.Net60)]
[SimpleJob(RuntimeMoniker.NetCoreApp31)]
[SimpleJob(RuntimeMoniker.Net48)]
[MeanColumn]
public class ArrayReadBenchmark {
    [Benchmark]
    public int For() {
        var sum = 0;
        for (var i = 0; i < _array.Length; i++) {
            sum += _array[i];
        }

        return sum;
    }

    [Benchmark(Baseline = true)]
    public int Foreach() {
        var sum = 0;
        foreach (var element in _array) {
            sum += element;
        }

        return sum;
    }

    //[Benchmark]
    //public int ForeachCustom() {
    //    var sum = 0;
    //    foreach (var element in new ArrayEnumerator<int>(_array)) {
    //        sum += element;
    //    }

    //    return sum;
    //}

    [Benchmark]
    public int ForeachSpan() {
        var sum = 0;
        foreach (var element in _array.AsSpan()) {
            sum += element;
        }

        return sum;
    }

    [Benchmark]
    public int ForUnsafeRef() {
        var sum = 0;
        ref int refStart = ref MemoryMarshal.GetReference<int>(_array);
        for (var i = 0; i < _array.Length; i++) {
            sum += Unsafe.Add(ref refStart, i);
        }
        return sum;
    }

    [Benchmark]
    public int ForUnsafe2Refs() {
        var sum = 0;
        for (ref int refItem = ref MemoryMarshal.GetReference<int>(_array),
                refEnd = ref Unsafe.Add(ref refItem, _array.Length);
            Unsafe.IsAddressLessThan(ref refItem, ref refEnd);
            refItem = ref Unsafe.Add(ref refItem, 1))
        {
            sum += refItem;
        }
        return sum;
    }

    [Benchmark]
    public unsafe int ForUnsafePointer() {
        var sum = 0;
        fixed (int* arrayPtr = &_array[0]) {
            for (var index = 0; index < _array.Length; index++) {
                sum += *(arrayPtr + index);
            }
        }

        return sum;
    }

    [Benchmark]
    public unsafe int ForUnsafe2Pointers() {
        var sum = 0;
        fixed (int* arrayPtr = _array) {
            for (int* ptr = arrayPtr,
                    endPtr = arrayPtr + _array.Length;
                ptr < endPtr;
                ptr++)
            {
                sum += *ptr;
            }
        }

        return sum;
    }

    #region Configuration

    private int[] _array = null!;

    [GlobalSetup]
    public void Init() {
        const int count = 1021;

        _array = new int[count];

        var rnd = new Random(1234);
        for (var i = 0; i < count; i++) {
            _array[i] = rnd.Next(0, 10);
        }
    }

    #endregion
}

ArrayReadBenchmark.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFrameworks>net8.0;net7.0;net6.0;netcoreapp3.1;net48;</TargetFrameworks>
    <LangVersion>10.0</LangVersion>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="BenchmarkDotNet" Version="0.13.5" />
  </ItemGroup>

</Project>

Program.cs

using BenchmarkDotNet.Running;
using Storage.Benchmark;

var _ = BenchmarkRunner.Run<ArrayReadBenchmark>(null!, args);