//! 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(v: &mut [T]) { let len = v.len(); if len <= 1 { return; } thread_local! { static RNG: Cell> = 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) { loop { match deadline { None => thread::sleep(Duration::from_secs(1000)), Some(d) => { let now = Instant::now(); if now >= d { break; } thread::sleep(d - now); } } } } // https://github.com/crossbeam-rs/crossbeam/issues/795 pub(crate) fn convert_timeout_to_deadline(timeout: Duration) -> Instant { match Instant::now().checked_add(timeout) { Some(deadline) => deadline, None => Instant::now() + Duration::from_secs(86400 * 365 * 30), } }