Oddities of the yosys $macc cell. To all "losses" in modifications, add in your head the necessity of creating a v2 cell with compatibility wrapping of some kind.
Length of the factor length fields, known as variable num_bits in docs and code, is recorded in the CONFIG parameter and capped at effectively 15. We can set it to const 16 for example, simplifying CONFIG parsing.
Gains: simplifies from_cell, to_cell, simlib.v,