Function small_order_encoding 

pub fn small_order_encoding(w: [b64; 4]) -> bool

The eight low-order encodings strict verification rejects.

The list is the one rhdl_ed25519_fast_core checks (see host::small_order_encoding): the identity (y = 1), the point of order 2 (y = p - 1), the two order-4 points (y = 0, both signs), and the four order-8 points (two y values, both signs). The comparison is on the encoding bytes, so it is only meaningful for canonical encodings.