//! sign-dist: time secp256k1 signing and keep every sample, so the distribution can be drawn.
//!
//! The same timed loop as sentinel-bench's emit_benchmark_json in the zerocopy workspace: the same key bytes,
//! the same 256-byte message, the same 1,000 warm-up signatures. It writes one duration per line, in
//! nanoseconds, in the order taken. Used for the histogram on https://zerocopy.systems/latency.
//!
//! Cargo.toml for a crate named sign-dist (the release profile matches the zerocopy workspace's):
//!
//!   [package]
//!   name = "sign-dist"
//!   version = "0.1.0"
//!   edition = "2021"
//!
//!   [dependencies]
//!   k256 = { version = "=0.13.4", features = ["ecdsa", "sha256"] }
//!
//!   [profile.release]
//!   opt-level = 3
//!   strip = true
//!   lto = "fat"
//!   panic = "abort"
//!   codegen-units = 1
//!   overflow-checks = true
//!
//! Put this file at src/main.rs, then:
//!   cargo build --release
//!   ./target/release/sign-dist 200000 > samples.txt
use k256::ecdsa::{signature::Signer, Signature, SigningKey};
use std::io::Write;
use std::time::Instant;

fn main() {
    let n: usize = std::env::args().nth(1).and_then(|v| v.parse().ok()).unwrap_or(200_000);
    let signing_key = SigningKey::from_bytes(&[42u8; 32].into()).expect("static key bytes are valid");
    let message = [0xABu8; 256];
    for _ in 0..1000 {
        let _: Signature = signing_key.sign(&message);
    }
    let mut samples: Vec<u64> = Vec::with_capacity(n);
    for _ in 0..n {
        let t0 = Instant::now();
        let s: Signature = signing_key.sign(&message);
        samples.push(t0.elapsed().as_nanos() as u64);
        std::hint::black_box(s);
    }
    let out = std::io::stdout();
    let mut w = std::io::BufWriter::new(out.lock());
    for s in samples {
        writeln!(w, "{s}").unwrap();
    }
}