OTP-004: Auto Encoder

This proposal defines a way to automatically build a serialization layout for a given structure.

Motivation

Designing a serialization layout in TLB is a very risky task. Developer have to take care of the size limitations of cells and remember how much bits are used by each field. This is a very error-prone task and it is very easy to make a mistake. This proposal aims to solve this problem by providing a way to automatically build a serialization layout for a given structure.

Specification

We are defining auto encoder as an eager algorithm that builds a serialization layout for a given structure. The algorithm is defined as follows:

Define available reference and bits in a current cell 
   as `available_references` and `available_bits` respectively.
   NOTE: there must be at least one reference reserved for serialization tail and one 
         bit for optional flag. Depending on context more references or bits may be reserved. 

For each field in A:
    (size_bits, size_ref) = get_field_max_size(field);
    if (available_bits >= size_bits && available_references >= size_ref) {
        Push field to a current cell
    } else {
        available_references = (1023 - 1);
        available_bits = (4 - 1);
        Allocate a new tail and continue from current field
    }

Drawbacks

• This is an implicit algorithm. It is not clear results of this allocator and have to be checked to make compatible serialization.