Implement a faster sort algorithm
This is a complete rewrite of the standard sort algorithm. The new algorithm is a simplified variant of TimSort. In summary, the changes are: * Improved performance, especially on partially sorted inputs. * Performs less comparisons on both random and partially sorted inputs. * Decreased the size of temporary memory: the new sort allocates 4x less.
This commit is contained in:
Stjepan Glavina
parent
ff261d3a6b
commit
c8d73ea68a
4 changed files with 490 additions and 325 deletions
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@ -17,86 +17,111 @@ use std::sync::atomic::{AtomicUsize, Ordering};
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use std::__rand::{thread_rng, Rng};
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use std::thread;
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const REPEATS: usize = 5;
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const MAX_LEN: usize = 32;
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static drop_counts: [AtomicUsize; MAX_LEN] =
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// FIXME #5244: AtomicUsize is not Copy.
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[
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AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0),
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AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0),
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AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0),
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AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0),
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AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0),
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AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0),
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AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0),
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AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0),
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AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0),
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AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0),
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AtomicUsize::new(0), AtomicUsize::new(0),
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];
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const MAX_LEN: usize = 80;
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static creation_count: AtomicUsize = AtomicUsize::new(0);
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static DROP_COUNTS: [AtomicUsize; MAX_LEN] = [
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// FIXME #5244: AtomicUsize is not Copy.
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AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0),
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AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0),
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AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0),
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AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0),
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AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0),
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AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0),
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AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0),
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AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0),
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AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0),
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AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0),
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AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0),
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AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0),
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AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0),
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AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0),
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AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0),
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AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0),
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AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0),
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AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0),
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AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0),
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AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0), AtomicUsize::new(0),
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];
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#[derive(Clone, PartialEq, PartialOrd, Eq, Ord)]
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struct DropCounter { x: u32, creation_id: usize }
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struct DropCounter {
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x: u32,
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id: usize,
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}
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impl Drop for DropCounter {
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fn drop(&mut self) {
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drop_counts[self.creation_id].fetch_add(1, Ordering::Relaxed);
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DROP_COUNTS[self.id].fetch_add(1, Ordering::Relaxed);
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}
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}
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pub fn main() {
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// len can't go above 64.
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for len in 2..MAX_LEN {
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for _ in 0..REPEATS {
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// reset the count for these new DropCounters, so their
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// IDs start from 0.
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creation_count.store(0, Ordering::Relaxed);
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fn test(input: &[DropCounter]) {
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let len = input.len();
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let mut rng = thread_rng();
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let main = (0..len).map(|_| {
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DropCounter {
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x: rng.next_u32(),
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creation_id: creation_count.fetch_add(1, Ordering::Relaxed),
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// Work out the total number of comparisons required to sort
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// this array...
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let mut count = 0usize;
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input.to_owned().sort_by(|a, b| { count += 1; a.cmp(b) });
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// ... and then panic on each and every single one.
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for panic_countdown in 0..count {
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// Refresh the counters.
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for i in 0..len {
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DROP_COUNTS[i].store(0, Ordering::Relaxed);
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}
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let v = input.to_owned();
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let _ = thread::spawn(move || {
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let mut v = v;
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let mut panic_countdown = panic_countdown;
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v.sort_by(|a, b| {
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if panic_countdown == 0 {
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panic!();
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}
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}).collect::<Vec<_>>();
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panic_countdown -= 1;
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a.cmp(b)
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})
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}).join();
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// work out the total number of comparisons required to sort
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// this array...
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let mut count = 0_usize;
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main.clone().sort_by(|a, b| { count += 1; a.cmp(b) });
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// ... and then panic on each and every single one.
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for panic_countdown in 0..count {
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// refresh the counters.
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for c in &drop_counts {
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c.store(0, Ordering::Relaxed);
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}
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let v = main.clone();
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let _ = thread::spawn(move|| {
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let mut v = v;
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let mut panic_countdown = panic_countdown;
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v.sort_by(|a, b| {
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if panic_countdown == 0 {
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panic!()
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}
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panic_countdown -= 1;
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a.cmp(b)
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})
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}).join();
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// check that the number of things dropped is exactly
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// what we expect (i.e. the contents of `v`).
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for (i, c) in drop_counts.iter().enumerate().take(len) {
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let count = c.load(Ordering::Relaxed);
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assert!(count == 1,
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"found drop count == {} for i == {}, len == {}",
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count, i, len);
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}
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}
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// Check that the number of things dropped is exactly
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// what we expect (i.e. the contents of `v`).
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for (i, c) in DROP_COUNTS.iter().enumerate().take(len) {
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let count = c.load(Ordering::Relaxed);
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assert!(count == 1,
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"found drop count == {} for i == {}, len == {}",
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count, i, len);
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}
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}
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}
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fn main() {
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for len in (1..20).chain(70..MAX_LEN) {
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// Test on a random array.
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let mut rng = thread_rng();
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let input = (0..len).map(|id| {
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DropCounter {
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x: rng.next_u32(),
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id: id,
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}
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}).collect::<Vec<_>>();
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test(&input);
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// Test on a sorted array with two elements randomly swapped, creating several natural
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// runs of random lengths. Such arrays have very high chances of hitting all code paths in
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// the merge procedure.
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for _ in 0..5 {
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let mut input = (0..len).map(|i|
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DropCounter {
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x: i as u32,
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id: i,
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}
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).collect::<Vec<_>>();
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let a = rng.gen::<usize>() % len;
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let b = rng.gen::<usize>() % len;
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input.swap(a, b);
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test(&input);
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}
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}
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}
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