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use std::fmt;
use std::time::{Instant, Duration};
const MIN_DUR: f64 = 1.0;
const MIN_TIMES: usize = 4;
pub struct Bench {
pub executions: usize,
pub duration: f64,
pub duration_stddev: f64,
}
impl fmt::Display for Bench {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(f, "{} secs ± {} ({}%)",
self.duration, self.duration_stddev, self.duration_stddev / self.duration * 100.0)
}
}
fn duration_secs(d: Duration) -> f64 {
d.as_secs() as f64 + d.subsec_nanos() as f64 / 1.0e9
}
// Returns estimate of single-iteration time
fn warmup<A, F: Fn() -> A>(func: F) -> f64 {
let mut ntimes = 1;
let mut time_taken = 0.0;
while time_taken < 0.5 {
let start = Instant::now();
for _ in 0..ntimes {
func();
}
let end = Instant::now();
time_taken = duration_secs(end - start);
ntimes *= 2;
}
time_taken / ntimes as f64
}
pub fn benchmark<A, F: Fn() -> A>(func: F) -> Bench {
let estimate = warmup(&func);
let ntimes_guess = if MIN_TIMES as f64 * estimate >= MIN_DUR {
MIN_TIMES
} else {
(MIN_DUR / estimate).ceil() as usize
};
let nparts = if ntimes_guess < 10 {
ntimes_guess
} else {
std::cmp::max(10, ntimes_guess / 10)
};
let nperpart = (ntimes_guess + nparts - 1) / nparts;
let ntimes = nparts * nperpart;
// eprintln!("BENCH: estimate={} ntimes_guess={} nparts={} nperpart={} ntimes={}", estimate, ntimes_guess, nparts, nperpart, ntimes);
let mut times = vec![0.0; nparts];
for i in 0..nparts {
let start = Instant::now();
for _ in 0..nperpart {
func();
}
let end = Instant::now();
times[i] = duration_secs(end - start);
}
let mean = times.iter().map(|&t| t).sum::<f64>() / ntimes as f64;
let stddev = times.iter().map(|t| (t - mean) * (t - mean)).sum::<f64>() / (ntimes - 1) as f64;
Bench { executions: 0, duration: mean, duration_stddev: stddev }
}
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