Function bilinear_wave 

pub fn bilinear_wave<V, T, R0, R1, RO>(
    h0: &mut ValueHistory<V, T, R0>,
    h1: &mut ValueHistory<V, T, R1>,
    emit: impl FnMut(V, V, T, RO),
)
where
    V: Copy + Ord,
    T: Ord + Clone + Lattice,
    R0: Semigroup + Multiply<R1, Output = RO> + Clone,
    R1: Semigroup + Clone,

Produces the join of two histories: every pair of edits, diffs multiplied and times joined, visited in time order. Repeatedly steps the history with the earlier un-replayed edit and multiplies it against the other’s buffer, which is consolidated under the meet of its remaining times as the wave advances — so work is bounded by the netted accumulation sizes rather than the raw history lengths.

emit receives every produced (id0, id1, joined time, multiplied diff). Both histories must be pre-loaded (load/load_iter) and are fully drained. For small histories a plain cross product is cheaper; callers should gate on size.