Where is the volumeToUserRange() equivalent in MS4?

Do you know how volume works in MS4 src?

I'm tring to get the hang of the new separated engine code structure.
Where is the volumeToUserRange() equivalent or default zero (MS3=100/127) in MS4 Mixer ?

static constexpr volume_dbfs_t MAX_DISPLAYED_DBFS = 0.f; // 100%
static constexpr volume_dbfs_t MIN_DISPLAYED_DBFS = -60.f; // 0%

SRC

Thanks

edit: re-phrased from earlier post, headroom is always 0.9