bench: bench register-pow for difficulty reference

blahd/benches/register-pow.rs

@@ -0,0 +1,56 @@
+#![expect(clippy::unwrap_used, reason = "allow in benches")]
+use std::hint::black_box;
+use std::time::Instant;
+
+use blah_types::{get_timestamp, PubKey, Signee, UserKey, UserRegisterPayload};
+use criterion::{criterion_group, criterion_main, Criterion};
+use ed25519_dalek::SigningKey;
+use rand::{thread_rng, Rng};
+use sha2::{Digest, Sha256};
+
+fn bench_register_pow(c: &mut Criterion) {
+    let rng = &mut thread_rng();
+
+    let id_key_priv = SigningKey::from_bytes(&[0x1A; 32]);
+    let id_key = PubKey(id_key_priv.verifying_key().to_bytes());
+    let act_key_priv = SigningKey::from_bytes(&[0x2B; 32]);
+    let act_key = PubKey(act_key_priv.verifying_key().to_bytes());
+    let payload = UserRegisterPayload {
+        id_key: id_key.clone(),
+        server_url: "http://some.example.com".parse().unwrap(),
+        id_url: "http://another.example.com".parse().unwrap(),
+        challenge_nonce: rng.gen(),
+    };
+    let mut signee = Signee {
+        nonce: 0,
+        payload,
+        timestamp: get_timestamp(),
+        user: UserKey { id_key, act_key },
+    };
+
+    c.bench_function("register_pow_iter", |b| {
+        b.iter_custom(|iters| {
+            signee.nonce = rng.gen();
+
+            let inst = Instant::now();
+            for _ in 0..iters {
+                let hash = {
+                    let signee = serde_jcs::to_string(&signee).unwrap();
+                    let mut h = Sha256::new();
+                    h.update(&signee);
+                    h.finalize()
+                };
+                let leading_zeros = hash
+                    .iter()
+                    .position(|&b| b != 0)
+                    .map_or(256, |i| i as u32 * 8 + hash[i].leading_zeros());
+                black_box(leading_zeros);
+                signee.nonce = signee.nonce.wrapping_add(1);
+            }
+            inst.elapsed()
+        });
+    });
+}
+
+criterion_group!(benches, bench_register_pow);
+criterion_main!(benches);