tor-netdoc: directory-signature: don't re-hash unnecessarily

            // Update the hash in self.$UPDATE according to algorithm $AGLO

            // (uses dynamic bindings of those parameters)

            ${define HASH {

                    // XXXX indentation is wrong

                // Avoid recalculating if we don't need to

                self.$UPDATE.get_or_insert_with(|| {

                    let mut h = tor_llcrypto::d::$ALGO::new();

                    h.update(body.body().body());

                    h.update(body.signature_item_kw_spc);

                    // XXXX Unconditionally write.  This can involve wasted work.

                    self.$UPDATE = Some(h.finalize().into());

                    h.finalize().into()

                });

            }}

            match &**algo {