benchs-string.Create.ps1

Invoke-RestMethod https://gist.githubusercontent.com/santisq/bd3d1d47c89f030be1b4e57b92baaddd/raw/aa78870a9674e9e4769b05e333586bf405c1362c/Measure-Expression.ps1 |
    Invoke-Expression

Add-Type @'
using System;
using System.Text;

public static class TestString
{
    public static string Create(string @string, int len) =>
        string.Create(length: len, state: @string, action: Action);

    private static void Action(Span<char> chars, string state)
    {
        int i = 0; int x = 0;
        bool prevSpace = false;

        foreach (char e in state.AsSpan())
        {
            if (i++ == chars.Length)
            {
                return;
            }

            if (char.IsWhiteSpace(e))
            {
                if (!prevSpace)
                {
                    chars[x++] = ' ';
                }

                prevSpace = true;
                continue;
            }

            chars[x++] = e;
            prevSpace = false;
        }
    }

    public static string Builder(string @string, int len)
    {
        StringBuilder sb = new(len);
        bool prevSpace = false;
        foreach (char e in @string)
        {
            if (sb.Length == len)
            {
                break;
            }

            if (char.IsWhiteSpace(e))
            {
                if (!prevSpace)
                {
                    sb.Append(' ');
                }
                prevSpace = true;
                continue;
            }

            sb.Append(e);
            prevSpace = false;
        }

        return sb.ToString();
    }
}
'@

$tests = @{
    'Regex Replace + SubString' = {
        param([string] $String, [int] $MaxLength)

        $Text = $String -Replace '\s+', ' '
        if ($Text.Length -gt $MaxLength) {
            $Text = $Text.SubString(0, $MaxLength)
        }
        $Text
    }
    'StringBuilder'             = {
        param([string] $String, [int] $MaxLength)

        $sb = [System.Text.StringBuilder]::new($MaxLength)

        foreach ($char in $String.GetEnumerator()) {
            if ($sb.Length -eq $MaxLength) {
                break
            }

            if ([char]::IsWhiteSpace($char)) {
                if (-not $prevSpace) {
                    $sb = $sb.Append(' ')
                }

                $prevSpace = $true
                continue
            }

            $sb = $sb.Append($char)
            $prevSpace = $false
        }

        $sb.ToString()
    }
    'StringBuilder (Compiled)'  = {
        param([string] $String, [int] $MaxLength)

        [TestString]::Builder($String, $MaxLength)
    }
    'String.Create'             = {
        param([string] $String, [int] $MaxLength)

        [TestString]::Create($String, $MaxLength)
    }
}

$sb = [System.Text.StringBuilder]::new()
1kb, 10kb, 50kb, 100kb, 500kb | ForEach-Object {
    $sb = $sb.Clear()

    foreach ($i in 0..$_) {
        $sb = $sb.Append('word' + ' ' * (Get-Random -Maximum 10))
    }

    Measure-Expression $tests -Parameters @{
        string    = $sb.ToString()
        maxlength = 1000
    } | Select-Object @{ N='WordCount'; E={ $sb.Length }}, *
} | Format-Table -GroupBy WordCount

maybefasterwithspan.cs

using System;

public static class TestString
{
    public static string Create(string @string, int len) =>
        string.Create(length: len, state: @string, action: Action);

    private static void Action(Span<char> chars, string state)
    {
        int i = 0;
        bool prevSpace = false;

        foreach (char e in state)
        {
            if (i == chars.Length)
            {
                return;
            }

            if (char.IsWhiteSpace(e))
            {
                if (!prevSpace)
                {
                    chars[i++] = ' ';
                }

                prevSpace = true;
                continue;
            }

            chars[i++] = e;
            prevSpace = false;
        }
    }
}

results.md

   WordCount: 1024

WordCount Test          Average RelativeSpeed
--------- ----          ------- -------------
     1024 Question      1.92 ms 1x
     1024 String.Create 3.32 ms 1.73x
     1024 StringBuilder 4.83 ms 2.51x

   WordCount: 10240

WordCount Test          Average RelativeSpeed
--------- ----          ------- -------------
    10240 String.Create 0.27 ms 1x
    10240 StringBuilder 0.39 ms 1.47x
    10240 Question      2.32 ms 8.71x

   WordCount: 51200

WordCount Test          Average  RelativeSpeed
--------- ----          -------  -------------
    51200 StringBuilder 0.45 ms  1x
    51200 String.Create 1.27 ms  2.79x
    51200 Question      13.05 ms 28.74x

   WordCount: 102400

WordCount Test          Average  RelativeSpeed
--------- ----          -------  -------------
   102400 StringBuilder 0.21 ms  1x
   102400 String.Create 1.99 ms  9.49x
   102400 Question      12.09 ms 57.57x

   WordCount: 512000

WordCount Test          Average  RelativeSpeed
--------- ----          -------  -------------
   512000 StringBuilder 0.25 ms  1x
   512000 String.Create 10.07 ms 40.59x
   512000 Question      58.96 ms 237.73x