float parsing

Program.cs

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;
using System.Buffers;
using System.Text.Json;

// prove impl
var obj = new MyBench { Count = 5 };
obj.Init();
Console.WriteLine(obj.Payload);
Console.WriteLine(string.Join(',', obj.Linq()));
Console.WriteLine(string.Join(',', obj.Json()));
Console.WriteLine(string.Join(',', obj.Manual()));

// bench
BenchmarkRunner.Run(typeof(MyBench).Assembly);

[MemoryDiagnoser]
public class MyBench
{
    [Params(1, 3, 20, 200)]
    public int Count { get; set; }

    [GlobalSetup]
    public void Init()
    {
        Random rand = new Random(1234151);
        Payload = "[" + string.Join(',', Enumerable.Range(0, Count).Select(x => rand.Next(0,1000) / rand.Next(0,3) switch
        {
            0 => 1f,
            1 => 10f,
            _ => 100f
        })) + "]";
    }

    public string Payload { get; private set; } = "[10,20.5,30.88]";

    [Benchmark]
    public float[] Linq() => Payload.Substring(1, Payload.Length-2).Split(',').Select(s => float.Parse(s)).ToArray();

    [Benchmark]
    public float[] Json() => JsonSerializer.Deserialize<float[]>(Payload)!;

    [Benchmark]
    public float[] Manual()
    {
        SequenceReader<char> r = new(new(Payload.AsMemory().Slice(1, Payload.Length - 2)));
        var copy = r;
        int count = 1; // count first
        while (r.TryAdvanceTo(',')) count++;

        // now repeat
        float[] arr = new float[count];
        r = copy;
        int i = 0;
        while (r.TryReadTo(out ReadOnlySpan<char> tok, ','))
        {
            arr[i++] = float.Parse(tok);
        }
        arr[i++] = float.Parse(r.UnreadSpan);
        return arr;
    }

}

Results.txt

| Method | Count | Mean        | Error     | StdDev    | Gen0   | Gen1   | Allocated |
|------- |------ |------------:|----------:|----------:|-------:|-------:|----------:|
| Linq   | 1     |    54.32 ns |  0.293 ns |  0.245 ns | 0.0086 |      - |     144 B |
| Json   | 1     |   113.54 ns |  0.336 ns |  0.298 ns | 0.0062 |      - |     104 B |
| Manual | 1     |    72.60 ns |  0.232 ns |  0.217 ns | 0.0019 |      - |      32 B |
| Linq   | 3     |   131.29 ns |  0.726 ns |  0.679 ns | 0.0167 |      - |     280 B |
| Json   | 3     |   182.91 ns |  1.264 ns |  1.182 ns | 0.0067 |      - |     112 B |
| Manual | 3     |   137.58 ns |  0.305 ns |  0.270 ns | 0.0024 |      - |      40 B |
| Linq   | 20    |   676.51 ns |  2.932 ns |  2.449 ns | 0.0706 |      - |    1184 B |
| Json   | 20    |   784.94 ns |  5.818 ns |  5.443 ns | 0.0277 |      - |     472 B |
| Manual | 20    |   913.55 ns |  4.204 ns |  3.932 ns | 0.0057 |      - |     104 B |
| Linq   | 200   | 6,868.95 ns | 81.107 ns | 75.868 ns | 0.6332 | 0.0076 |   10664 B |
| Json   | 200   | 6,634.72 ns | 43.096 ns | 40.312 ns | 0.1755 |      - |    3056 B |
| Manual | 200   | 8,923.92 ns | 21.489 ns | 17.944 ns | 0.0458 |      - |     824 B |