Function certify_linear 

pub fn certify_linear(n: u32, rows: &[u64]) -> bool

Certify a purely-LINEAR n-bit block reversible: its GF(2) transfer matrix (rows[v] a bitmask of which input bits XOR into output bit v) must be invertible (∈ GL(n,2)), giving a linear inverse. This is the fast path for CNOT-only (XOR) datapaths.