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Disable Quick JIT

From .NET 7 onwards, to disable Quick JIT, edit the application project file (.csproj) as follows.

<Project Sdk="Microsoft.NET.Sdk">
  ...
  <PropertyGroup>
    ...
    <TieredCompilationQuickJit>false</TieredCompilationQuickJit>
    ...
  </PropertyGroup>
  ...
</Project>

Application startup time increases, but optimisation improves and runtime performance should be faster.

Reference: https://qiita.com/rougemeilland/items/b8b4b045b82a294a56de

Checking 0 <= n && n < MAX for an integer n

Instead of writing:

if (n >= 0 && n < MAX)

prefer:

if ((uint)n < (uint)MAX)

This reduces the number of comparisons. The cast to uint has virtually no overhead.

ArrayPool<T>.Shared

For temporary arrays used inside loops or similar contexts, avoid new[] and instead rent from the shared pool as shown below. This is more memory-efficient, faster, and avoids GC pressure.

byte[] array = ArrayPool<byte>.Shared.Rent(20); // Rent a buffer

// ... use array ...

ArrayPool<byte>.Shared.Return(array); // Return the borrowed buffer

Reference: https://ikorin2.hatenablog.jp/entry/2021/12/20/225208

.Where(…).Select(…)

Always chain .Where() before .Select(). The JIT compiler can optimise this ordering.

Debug branching without #if DEBUG

Define the following static class and use AssemblyState.IsDebug in conditional expressions.

internal static class AssemblyState {
  public const bool IsDebug =>
  #if DEBUG
    true;
  #else
    false;
  #endif
}

This keeps the code concise and has no effect on runtime performance.

Reference: https://ikorin2.hatenablog.jp/entry/2020/06/27/065646

Returning ordinal strings (1st, 2nd, 3rd, …)

public static string Ordinal(this int number)
{
    var ones = number % 10;
    var tens = Math.Floor(number / 10f) % 10;
    if (tens == 1)
        return number + "th";
    else return ones switch
    {
        1 => number + "st",
        2 => number + "nd",
        3 => number + "rd",
        _ => number + "th",
    };
}