Optimize MemoryMarshal.ToEnumerable for arrays and strings

[stephentoub]

Method	Toolchain	Length	Mean	Ratio	Allocated	Alloc Ratio
CountArrayLINQ	\main\corerun.exe	1	32.808 ns	1.00	64 B	1.00
CountArrayLINQ	\pr\corerun.exe	1	9.272 ns	0.28	-	0.00
CountArray	\main\corerun.exe	1	21.079 ns	1.00	64 B	1.00
CountArray	\pr\corerun.exe	1	13.257 ns	0.63	32 B	0.50
CountArraySlice	\main\corerun.exe	1	17.804 ns	1.00	64 B	1.00
CountArraySlice	\pr\corerun.exe	1	5.121 ns	0.29	-	0.00
CountNonArray	\main\corerun.exe	1	23.013 ns	1.00	64 B	1.00
CountNonArray	\pr\corerun.exe	1	24.884 ns	1.08	64 B	1.00
CountArrayLINQ	\main\corerun.exe	1000	3,129.629 ns	1.000	64 B	1.00
CountArrayLINQ	\pr\corerun.exe	1000	9.484 ns	0.003	-	0.00
CountArray	\main\corerun.exe	1000	3,627.104 ns	1.00	64 B	1.00
CountArray	\pr\corerun.exe	1000	1,400.046 ns	0.41	32 B	0.50
CountArraySlice	\main\corerun.exe	1000	3,579.278 ns	1.00	64 B	1.00
CountArraySlice	\pr\corerun.exe	1000	1,920.087 ns	0.54	64 B	1.00
CountNonArray	\main\corerun.exe	1000	5,087.494 ns	1.00	64 B	1.00
CountNonArray	\pr\corerun.exe	1000	4,562.180 ns	0.90	64 B	1.00

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;
using System;
using System.Buffers;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;

BenchmarkSwitcher.FromAssembly(typeof(Tests).Assembly).Run(args);

[MemoryDiagnoser(false)]
public class Tests
{
    private Memory<char> _array;
    private Memory<char> _arraySlice;
    private Memory<char> _nonArray;

    [Params(1, 1000)]
    public int Length { get; set; }

    [GlobalSetup]
    public void Setup()
    {
        _array = Enumerable.Repeat('a', Length).ToArray();
        _arraySlice = _array.Slice(1);
        _nonArray = new WrapperMemoryManager<char>(_array).Memory;
    }

    [Benchmark]
    public int CountArrayLINQ() => Enumerable.Count(MemoryMarshal.ToEnumerable<char>(_array));

    [Benchmark]
    public int CountArray() => Count(MemoryMarshal.ToEnumerable<char>(_array));

    [Benchmark]
    public int CountArraySlice() => Count(MemoryMarshal.ToEnumerable<char>(_arraySlice));

    [Benchmark]
    public int CountNonArray() => Count(MemoryMarshal.ToEnumerable<char>(_nonArray));

    private static int Count<T>(IEnumerable<T> source)
    {
        int count = 0;
        foreach (T item in source) count++;
        return count;
    }

    private sealed class WrapperMemoryManager<T>(Memory<T> memory) : MemoryManager<T>
    {
        public override Span<T> GetSpan() => memory.Span;
        public override MemoryHandle Pin(int elementIndex = 0) => throw new NotSupportedException();
        public override void Unpin() => throw new NotSupportedException();
        protected override void Dispose(bool disposing) { }
    }
}

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Issue Details

---

Method	Toolchain	Length	Mean	Ratio	Allocated	Alloc Ratio
CountArrayLINQ	\main\corerun.exe	1	32.808 ns	1.00	64 B	1.00
CountArrayLINQ	\pr\corerun.exe	1	9.272 ns	0.28	-	0.00
CountArray	\main\corerun.exe	1	21.079 ns	1.00	64 B	1.00
CountArray	\pr\corerun.exe	1	13.257 ns	0.63	32 B	0.50
CountArraySlice	\main\corerun.exe	1	17.804 ns	1.00	64 B	1.00
CountArraySlice	\pr\corerun.exe	1	5.121 ns	0.29	-	0.00
CountNonArray	\main\corerun.exe	1	23.013 ns	1.00	64 B	1.00
CountNonArray	\pr\corerun.exe	1	24.884 ns	1.08	64 B	1.00
CountArrayLINQ	\main\corerun.exe	1000	3,129.629 ns	1.000	64 B	1.00
CountArrayLINQ	\pr\corerun.exe	1000	9.484 ns	0.003	-	0.00
CountArray	\main\corerun.exe	1000	3,627.104 ns	1.00	64 B	1.00
CountArray	\pr\corerun.exe	1000	1,400.046 ns	0.41	32 B	0.50
CountArraySlice	\main\corerun.exe	1000	3,579.278 ns	1.00	64 B	1.00
CountArraySlice	\pr\corerun.exe	1000	1,920.087 ns	0.54	64 B	1.00
CountNonArray	\main\corerun.exe	1000	5,087.494 ns	1.00	64 B	1.00
CountNonArray	\pr\corerun.exe	1000	4,562.180 ns	0.90	64 B	1.00

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;
using System;
using System.Buffers;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;

BenchmarkSwitcher.FromAssembly(typeof(Tests).Assembly).Run(args);

[MemoryDiagnoser(false)]
public class Tests
{
    private Memory<char> _array;
    private Memory<char> _arraySlice;
    private Memory<char> _nonArray;

    [Params(1, 1000)]
    public int Length { get; set; }

    [GlobalSetup]
    public void Setup()
    {
        _array = Enumerable.Repeat('a', Length).ToArray();
        _arraySlice = _array.Slice(1);
        _nonArray = new WrapperMemoryManager<char>(_array).Memory;
    }

    [Benchmark]
    public int CountArrayLINQ() => Enumerable.Count(MemoryMarshal.ToEnumerable<char>(_array));

    [Benchmark]
    public int CountArray() => Count(MemoryMarshal.ToEnumerable<char>(_array));

    [Benchmark]
    public int CountArraySlice() => Count(MemoryMarshal.ToEnumerable<char>(_arraySlice));

    [Benchmark]
    public int CountNonArray() => Count(MemoryMarshal.ToEnumerable<char>(_nonArray));

    private static int Count<T>(IEnumerable<T> source)
    {
        int count = 0;
        foreach (T item in source) count++;
        return count;
    }

    private sealed class WrapperMemoryManager<T>(Memory<T> memory) : MemoryManager<T>
    {
        public override Span<T> GetSpan() => memory.Span;
        public override MemoryHandle Pin(int elementIndex = 0) => throw new NotSupportedException();
        public override void Unpin() => throw new NotSupportedException();
        protected override void Dispose(bool disposing) { }
    }
}

Author:	stephentoub
Assignees:	-
Labels:	area-System.Memory
Milestone:	-