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//! Miscellaneous utilities.
use std::cell::Cell;
use std::num::Wrapping;
use std::thread;
use std::time::{Duration, Instant};
/// Randomly shuffles a slice.
pub(crate) fn shuffle<T>(v: &mut [T]) {
let len = v.len();
if len <= 1 {
return;
}
thread_local! {
static RNG: Cell<Wrapping<u32>> = Cell::new(Wrapping(1_406_868_647));
}
let _ = RNG.try_with(|rng| {
for i in 1..len {
// This is the 32-bit variant of Xorshift.
//
// Source: https://en.wikipedia.org/wiki/Xorshift
let mut x = rng.get();
x ^= x << 13;
x ^= x >> 17;
x ^= x << 5;
rng.set(x);
let x = x.0;
let n = i + 1;
// This is a fast alternative to `let j = x % n`.
//
// Author: Daniel Lemire
// Source: https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction/
let j = ((x as u64).wrapping_mul(n as u64) >> 32) as u32 as usize;
v.swap(i, j);
}
});
}
/// Sleeps until the deadline, or forever if the deadline isn't specified.
pub(crate) fn sleep_until(deadline: Option<Instant>) {
loop {
match deadline {
None => thread::sleep(Duration::from_secs(1000)),
Some(d) => {
let now = Instant::now();
if now >= d {
break;
}
thread::sleep(d - now);
}
}
}
}
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