ArrayCopy

using System;
using System.Linq;
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Jobs;

namespace Benchmarks.CollectionBenchmarks;

[SimpleJob(RuntimeMoniker.Net80)]
[MeanColumn, MemoryDiagnoser]
public class ArrayCopy
{
    [Benchmark(Baseline = true)]
    public int Framework()
    {
        Array.Copy(_array, _result, _array.Length);
        return _result[0] % 2;
    }
    
    [Benchmark]
    public int Manual()
    {
        for (var i = _array.Length - 1; i >= 0; i--)
        {
            _result[i] = _array[i];
        }
    
        return _array[0] % 2;
    }

    [Benchmark]
    public int ManualBuffer()
    {
        Span<int> buffer = stackalloc int[256];

        var bufferIndex = 0;
        var bufferLength = buffer.Length;
        var part = 0;

        foreach (var element in _array)
        {
            buffer[bufferIndex++] = element;
            if (bufferIndex < bufferLength) continue;

            var target = _result.AsSpan(bufferIndex * part, bufferLength);
            part++;
            buffer.CopyTo(target);
            bufferIndex = 0;
        }

        return _array[0] % 2;
    }

    private int[] _array = null!;
    private int[] _result = null!;

    [GlobalSetup]
    public void Init()
    {
        _array = Enumerable.Range(0, 10_000).ToArray();
        _result = new int[_array.Length];
    }
}