Lib.rs

Wrapping is compacted into a u32 to be Copy. It's copied at various places to keep track of current wrapping. It's functionally equivalent to:

struct Wrapping {
  inner_is_required: bool,
  /// Innermost to outermost.
  list_wrappings: VecDeque<ListWrapping>
}

Since ListWrapping has only two cases and we won't encounter absurd levels of wrapping, we can bitpack it. The current structure supports up to 21 list_wrappings.

It's structured as follows:

       start (5 bits)
       ↓               ↓ list_wrapping (1 == Required / 0 == Nullable)
   ┌────┐      ┌────────────────────────┐
  0000_0000_0000_0000_0000_0000_0000_0000
         └────┘
            ↑ end (5 bits)
  ↑
  inner_is_required flag (1 == required)

The list_wrapping is stored from innermost to outermost and use the start and end as the positions within the list_wrapping bits. Acting like a simplified fixed capacity VecDeque. For simplicity of bit shifts the list wrapping is stored from right to left.