Fill chunk

Program.cs

using System;
using System.Diagnostics;
using System.Runtime.Intrinsics.X86;

public class Program
{
    public static void Main()
    {
        uint NumPrefixHexDigits(uint dataLength) => (35 - Lzcnt.LeadingZeroCount(dataLength)) / 4;

        uint lastPrefixSize = 0;

        for (uint sizeAvailable = 6; sizeAvailable <= int.MaxValue; sizeAvailable++)
        {
            var candidate1PrefixSize = NumPrefixHexDigits(sizeAvailable);
            var candidate1DataSize = sizeAvailable - candidate1PrefixSize - 4;
            var candidate2PrefixSize = NumPrefixHexDigits(candidate1DataSize);

            if (candidate1PrefixSize != candidate2PrefixSize)
            {
                var candidate2DataSize = sizeAvailable - candidate2PrefixSize - 4;
                var candidate3PrefixSize = NumPrefixHexDigits(candidate2DataSize);

                if (candidate3PrefixSize != candidate2PrefixSize)
                {
                    Trace.Assert(candidate3PrefixSize == candidate2PrefixSize + 1);

                    Console.WriteLine($"Given {sizeAvailable} bytes from underlying PipeWriter, slice 1 extra byte off end of actualMemory.");
                }
            }

            if (candidate2PrefixSize != lastPrefixSize)
            {
                lastPrefixSize = candidate2PrefixSize;
                Console.WriteLine($"Starting at {sizeAvailable} bytes from underlying PipeWriter, expect prefix to be {candidate2PrefixSize} hex digits.");
            }
        }
    }
}

stdout

> dotnet run -c Release
Starting at 6 bytes from underlying PipeWriter, expect prefix to be 1 hex digits.
Given 21 bytes from underlying PipeWriter, slice 1 extra byte off end of actualMemory.
Starting at 22 bytes from underlying PipeWriter, expect prefix to be 2 hex digits.
Given 262 bytes from underlying PipeWriter, slice 1 extra byte off end of actualMemory.
Starting at 263 bytes from underlying PipeWriter, expect prefix to be 3 hex digits.
Given 4103 bytes from underlying PipeWriter, slice 1 extra byte off end of actualMemory.
Starting at 4104 bytes from underlying PipeWriter, expect prefix to be 4 hex digits.
Given 65544 bytes from underlying PipeWriter, slice 1 extra byte off end of actualMemory.
Starting at 65545 bytes from underlying PipeWriter, expect prefix to be 5 hex digits.
Given 1048585 bytes from underlying PipeWriter, slice 1 extra byte off end of actualMemory.
Starting at 1048586 bytes from underlying PipeWriter, expect prefix to be 6 hex digits.
Given 16777226 bytes from underlying PipeWriter, slice 1 extra byte off end of actualMemory.
Starting at 16777227 bytes from underlying PipeWriter, expect prefix to be 7 hex digits.
Given 268435467 bytes from underlying PipeWriter, slice 1 extra byte off end of actualMemory.
Starting at 268435468 bytes from underlying PipeWriter, expect prefix to be 8 hex digits.