stackalloc is a relatively new keyword added to C#. It allows you to allocate a block of memory on the stack. Stack-allocated memory is a super-fast way to get a chunk of memory and is automatically discarded when the method returns. It's super fast because it's not allocated on the heap and does not need to be garbage collected. A stackalloc expression can be assigned to a variable of type Span<> or ReadOnlySpan<>, or to a pointer of that type if the unsafe keyword is used.
The stack has a limited amount of memory, so do not use this expression for larger chunks of memory. It will not work. Thankfully, if needed, normal heap allocation can also be assigned to Span<T>, so a nice one-liner can be used regardless of whether stackalloc is used or not.
Docs 📑: https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/stackalloc
Have you been using stackalloc?
const int MaxStackLimit = 1024;
Span<byte> buffer = inputLength <= MaxStackLimit ? stackalloc byte[MaxStackLimit] : new byte[inputLength];