1 files changed, 85 insertions, 0 deletions
diff --git a/third_party/rust/ryu/examples/upstream_benchmark.rs b/third_party/rust/ryu/examples/upstream_benchmark.rs
new file mode 100644
index 0000000000..437855bdc7
--- /dev/null
+++ b/third_party/rust/ryu/examples/upstream_benchmark.rs
@@ -0,0 +1,85 @@
+// cargo run --example upstream_benchmark --release
+
+use rand::{Rng, SeedableRng};
+
+const SAMPLES: usize = 10000;
+const ITERATIONS: usize = 1000;
+
+struct MeanAndVariance {
+    n: i64,
+    mean: f64,
+    m2: f64,
+}
+
+impl MeanAndVariance {
+    fn new() -> Self {
+        MeanAndVariance {
+            n: 0,
+            mean: 0.0,
+            m2: 0.0,
+        }
+    }
+
+    fn update(&mut self, x: f64) {
+        self.n += 1;
+        let d = x - self.mean;
+        self.mean += d / self.n as f64;
+        let d2 = x - self.mean;
+        self.m2 += d * d2;
+    }
+
+    fn variance(&self) -> f64 {
+        self.m2 / (self.n - 1) as f64
+    }
+
+    fn stddev(&self) -> f64 {
+        self.variance().sqrt()
+    }
+}
+
+macro_rules! benchmark {
+    ($name:ident, $ty:ident) => {
+        fn $name() -> usize {
+            let mut rng = rand_xorshift::XorShiftRng::from_seed([123u8; 16]);
+            let mut mv = MeanAndVariance::new();
+            let mut throwaway = 0;
+            for _ in 0..SAMPLES {
+                let f = loop {
+                    let f = $ty::from_bits(rng.gen());
+                    if f.is_finite() {
+                        break f;
+                    }
+                };
+
+                let t1 = std::time::SystemTime::now();
+                for _ in 0..ITERATIONS {
+                    throwaway += ryu::Buffer::new().format_finite(f).len();
+                }
+                let duration = t1.elapsed().unwrap();
+                let nanos = duration.as_secs() * 1_000_000_000 + duration.subsec_nanos() as u64;
+                mv.update(nanos as f64 / ITERATIONS as f64);
+            }
+            println!(
+                "{:12} {:8.3} {:8.3}",
+                concat!(stringify!($name), ":"),
+                mv.mean,
+                mv.stddev(),
+            );
+            throwaway
+        }
+    };
+}
+
+benchmark!(pretty32, f32);
+benchmark!(pretty64, f64);
+
+fn main() {
+    println!("{:>20}{:>9}", "Average", "Stddev");
+    let mut throwaway = 0;
+    throwaway += pretty32();
+    throwaway += pretty64();
+    if std::env::var_os("ryu-benchmark").is_some() {
+        // Prevent the compiler from optimizing the code away.
+        println!("{}", throwaway);
+    }
+}