pub fn split_entry(index: b6) -> (b5, b2)Expand description
(entry, coordinate) of a digit-table output index 3e + c.
e is the 0-based entry (the table point (e + 1) * Q), c the Niels
coordinate (0 y+x, 1 y-x, 2 2dxy). Computed by comparing index
with all 48 constant values rather than dividing by 3.