ArrayIteration.cs

using System.Linq;
using System.Runtime.CompilerServices;
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Order;

namespace Benchmarkator.Collections.Iteration;

[Orderer(SummaryOrderPolicy.FastestToSlowest)]
public class ArrayIteration
{
    [Params(4096)]
    public int Length;

    private int[] _data = null!;

    [GlobalSetup]
    public void Setup()
    {
        _data = Enumerable.Range(0, Length).ToArray();
    }

    [Benchmark]
    public int ForLoopAccessIndex()
    {
        var arr = _data;
        var item = 0;
        for (var i = 0; i < arr.Length; i++)
        {
            item = arr[i];
        }

        return item;
    }

    [Benchmark]
    public unsafe int ForLoopAccessPtr()
    {
        var arr = _data;
        var item = 0;

        // to get value on given index, `i` is added to address of first item
        // (`i` offsets pointer by size of `int*`)
        fixed (int* a = &arr[0])
        {
            for (var i = 0; i < arr.Length; i++)
            {
                item = *(a + i);
            }
        }

        return item;
    }

    [Benchmark]
    public int ForLoopAccessRef()
    {
        var arr = _data;
        var item = 0;

        // to get value on given index, `i` is added to reference to first item
        // (`i` offsets pointer by size of `ref int`)
        ref var first = ref arr[0];
        for (var i = 0; i < arr.Length; i++)
        {
            item = Unsafe.Add(ref first, i);
        }

        return item;
    }

    [Benchmark]
    public unsafe int WhileLoopAccessPtr()
    {
        var arr = _data;
        var item = 0;

        // move `tmp` in array, from first to last address
        // (pointer to `tmp` is moved to next field each iteration)
        fixed (int* a = &arr[0])
        {
            var last = a + arr.Length;
            var tmp = a;
            while (tmp < last)
            {
                item = *tmp;
                tmp += 1;
            }
        }

        return item;
    }

    [Benchmark]
    public int WhileLoopAccessRef()
    {
        var arr = _data;
        var item = 0;

        // move `temp` in array, from first to last reference
        // (reference to `tmp` is moved to next field each iteration)
        ref var temp = ref arr[0];
        ref var last = ref arr[arr.Length - 1];
        while (Unsafe.IsAddressLessThan(ref temp, ref last) || Unsafe.AreSame(ref temp, ref last))
        {
            item = temp;
            temp = ref Unsafe.Add(ref temp, 1);
        }

        return item;
    }
}