pub fn chain_step_digest_kernel(
state: [b8; 64],
feed_forward: [b8; 18],
) -> [b8; 18]Expand description
Final feed-forward: the 18 kept digest bytes of a finished state.
Inputs: the 64-byte state after the last stage and the 18 saved input
bytes. Output: the next 18-byte node, state[DIGEST_BYTES[i]] ⊕ feed[i].
Combinational: one XOR per output bit (18 × 8). Because only 18 bytes
are read, the S-boxes that feed only the other 46 bytes have no load and
are deleted.