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    //! Benchmarking module.
    pub use std::hint::black_box;

    use super::{
        event::CompletedTest,
        helpers::sink::Sink,
        options::BenchMode,
        types::TestDesc,
        test_result::TestResult,
        Sender,
    };

    use crate::stats;
    use std::time::{Duration, Instant};
    use std::cmp;
    use std::io;
    use std::panic::{catch_unwind, AssertUnwindSafe};
    use std::sync::{Arc, Mutex};

    /// Manager of the benchmarking runs.
    ///
    /// This is fed into functions marked with `#[bench]` to allow for
    /// set-up & tear-down before running a piece of code repeatedly via a
    /// call to `iter`.
    #[derive(Clone)]
    pub struct Bencher {
        mode: BenchMode,
        summary: Option<stats::Summary>,
        pub bytes: u64,
    }

    impl Bencher {
        /// Callback for benchmark functions to run in their body.
        pub fn iter<T, F>(&mut self, mut inner: F)
        where
            F: FnMut() -> T,
        {
            if self.mode == BenchMode::Single {
                ns_iter_inner(&mut inner, 1);
                return;
            }

            self.summary = Some(iter(&mut inner));
        }

        pub fn bench<F>(&mut self, mut f: F) -> Option<stats::Summary>
        where
            F: FnMut(&mut Bencher),
        {
            f(self);
            self.summary
        }
    }

    #[derive(Debug, Clone, PartialEq)]
    pub struct BenchSamples {
        pub ns_iter_summ: stats::Summary,
        pub mb_s: usize,
    }

    pub fn fmt_bench_samples(bs: &BenchSamples) -> String {
        use std::fmt::Write;
        let mut output = String::new();

        let median = bs.ns_iter_summ.median as usize;
        let deviation = (bs.ns_iter_summ.max - bs.ns_iter_summ.min) as usize;

        output
            .write_fmt(format_args!(
                "{:>11} ns/iter (+/- {})",
                fmt_thousands_sep(median, ','),
                fmt_thousands_sep(deviation, ',')
            ))
            .unwrap();
        if bs.mb_s != 0 {
            output
                .write_fmt(format_args!(" = {} MB/s", bs.mb_s))
                .unwrap();
        }
        output
    }

    // Format a number with thousands separators
    fn fmt_thousands_sep(mut n: usize, sep: char) -> String {
        use std::fmt::Write;
        let mut output = String::new();
        let mut trailing = false;
        for &pow in &[9, 6, 3, 0] {
            let base = 10_usize.pow(pow);
            if pow == 0 || trailing || n / base != 0 {
                if !trailing {
                    output.write_fmt(format_args!("{}", n / base)).unwrap();
                } else {
                    output.write_fmt(format_args!("{:03}", n / base)).unwrap();
                }
                if pow != 0 {
                    output.push(sep);
                }
                trailing = true;
            }
            n %= base;
        }

        output
    }

    fn ns_from_dur(dur: Duration) -> u64 {
        dur.as_secs() * 1_000_000_000 + (dur.subsec_nanos() as u64)
    }

    fn ns_iter_inner<T, F>(inner: &mut F, k: u64) -> u64
    where
        F: FnMut() -> T,
    {
        let start = Instant::now();
        for _ in 0..k {
            black_box(inner());
        }
        ns_from_dur(start.elapsed())
    }

    pub fn iter<T, F>(inner: &mut F) -> stats::Summary
    where
        F: FnMut() -> T,
    {
        // Initial bench run to get ballpark figure.
        let ns_single = ns_iter_inner(inner, 1);

        // Try to estimate iter count for 1ms falling back to 1m
        // iterations if first run took < 1ns.
        let ns_target_total = 1_000_000; // 1ms
        let mut n = ns_target_total / cmp::max(1, ns_single);

        // if the first run took more than 1ms we don't want to just
        // be left doing 0 iterations on every loop. The unfortunate
        // side effect of not being able to do as many runs is
        // automatically handled by the statistical analysis below
        // (i.e., larger error bars).
        n = cmp::max(1, n);

        let mut total_run = Duration::new(0, 0);
        let samples: &mut [f64] = &mut [0.0_f64; 50];
        loop {
            let loop_start = Instant::now();

            for p in &mut *samples {
                *p = ns_iter_inner(inner, n) as f64 / n as f64;
            }

            stats::winsorize(samples, 5.0);
            let summ = stats::Summary::new(samples);

            for p in &mut *samples {
                let ns = ns_iter_inner(inner, 5 * n);
                *p = ns as f64 / (5 * n) as f64;
            }

            stats::winsorize(samples, 5.0);
            let summ5 = stats::Summary::new(samples);

            let loop_run = loop_start.elapsed();

            // If we've run for 100ms and seem to have converged to a
            // stable median.
            if loop_run > Duration::from_millis(100)
                && summ.median_abs_dev_pct < 1.0
                && summ.median - summ5.median < summ5.median_abs_dev
            {
                return summ5;
            }

            total_run = total_run + loop_run;
            // Longest we ever run for is 3s.
            if total_run > Duration::from_secs(3) {
                return summ5;
            }

            // If we overflow here just return the results so far. We check a
            // multiplier of 10 because we're about to multiply by 2 and the
            // next iteration of the loop will also multiply by 5 (to calculate
            // the summ5 result)
            n = match n.checked_mul(10) {
                Some(_) => n * 2,
                None => {
                    return summ5;
                }
            };
        }
    }

    pub fn benchmark<F>(desc: TestDesc, monitor_ch: Sender<CompletedTest>, nocapture: bool, f: F)
    where
        F: FnMut(&mut Bencher),
    {
        let mut bs = Bencher {
            mode: BenchMode::Auto,
            summary: None,
            bytes: 0,
        };

        let data = Arc::new(Mutex::new(Vec::new()));
        let oldio = if !nocapture {
            Some((
                io::set_print(Some(Sink::new_boxed(&data))),
                io::set_panic(Some(Sink::new_boxed(&data))),
            ))
        } else {
            None
        };

        let result = catch_unwind(AssertUnwindSafe(|| bs.bench(f)));

        if let Some((printio, panicio)) = oldio {
            io::set_print(printio);
            io::set_panic(panicio);
        }

        let test_result = match result {
            //bs.bench(f) {
            Ok(Some(ns_iter_summ)) => {
                let ns_iter = cmp::max(ns_iter_summ.median as u64, 1);
                let mb_s = bs.bytes * 1000 / ns_iter;

                let bs = BenchSamples {
                    ns_iter_summ,
                    mb_s: mb_s as usize,
                };
                TestResult::TrBench(bs)
            }
            Ok(None) => {
                // iter not called, so no data.
                // FIXME: error in this case?
                let samples: &mut [f64] = &mut [0.0_f64; 1];
                let bs = BenchSamples {
                    ns_iter_summ: stats::Summary::new(samples),
                    mb_s: 0,
                };
                TestResult::TrBench(bs)
            }
            Err(_) => TestResult::TrFailed,
        };

        let stdout = data.lock().unwrap().to_vec();
        let message = CompletedTest::new(desc, test_result, None, stdout);
        monitor_ch.send(message).unwrap();
    }

    pub fn run_once<F>(f: F)
    where
        F: FnMut(&mut Bencher),
    {
        let mut bs = Bencher {
            mode: BenchMode::Single,
            summary: None,
            bytes: 0,
        };
        bs.bench(f);
    }