1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428
// Copyright (c) 2017 Emil Ernerfeldt
use std::cmp::Ordering;
use std::ptr;
// ----------------------------------------------------------------------------
/// This speeds up well-ordered input by quite a lot.
const DOUBLE_COMPARISONS: bool = true;
/// Low RECENCY = faster when there is low disorder (a lot of order).
/// High RECENCY = more resilient against long stretches of noise.
/// If RECENCY is too small we are more dependent on nice data/luck.
const RECENCY: usize = 8;
/// Back-track several elements at once. This is helpful when there are big clumps out-of-order.
const FAST_BACKTRACKING: bool = true;
/// Break early if we notice that the input is not ordered enough.
const EARLY_OUT: bool = true;
/// Test for early-out when we have processed len / `EARLY_OUT_TEST_AT` elements.
const EARLY_OUT_TEST_AT: usize = 4;
/// If more than this percentage of elements have been dropped, we abort.
const EARLY_OUT_DISORDER_FRACTION: f32 = 0.60;
// ----------------------------------------------------------------------------
/// This is the readable reference implementation that only works for Copy types.
/// Returns the number of dropped elements for diagnostic purposes.
fn sort_copy_by<T, F>(slice: &mut [T], mut compare: F) -> usize
where
T: Copy,
F: FnMut(&T, &T) -> Ordering,
{
if slice.len() < 2 {
return slice.len();
}
// ------------------------------------------------------------------------
// First step: heuristically find the Longest Nondecreasing Subsequence (LNS).
// The LNS is shifted into slice[..write] while slice[write..] will be left unchanged.
// Elements not part of the LNS will be put in the "dropped" vector.
let mut dropped = Vec::new();
let mut num_dropped_in_row = 0;
let mut write = 0; // Index of where to write the next element to keep.
let mut read = 0; // Index of the input stream.
let mut iteration = 0;
let ealy_out_stop = slice.len() / EARLY_OUT_TEST_AT;
while read < slice.len() {
iteration += 1;
if EARLY_OUT
&& iteration == ealy_out_stop
&& dropped.len() as f32 > read as f32 * EARLY_OUT_DISORDER_FRACTION
{
// We have seen a lot of the elements and dropped a lot of them.
// This doesn't look good. Abort.
for (i, &element) in dropped.iter().enumerate() {
slice[write + i] = element;
}
slice.sort_unstable_by(|a, b| compare(a, b));
return dropped.len() * EARLY_OUT_TEST_AT; // Just an estimate.
}
if write == 0 || compare(&slice[read], &slice[write - 1]) != Ordering::Less {
// The element is order - keep it:
slice[write] = slice[read];
read += 1;
write += 1;
num_dropped_in_row = 0;
} else {
// The next element is smaller than the last stored one.
// The question is - should we drop the new element, or was accepting the previous element a mistake?
/*
Check this situation:
. 0 1 2 3 9 5 6 7 (the 9 is a one-off)
. | |
. | read
. write - 1
Checking this improves performance because we catch common problems earlier (without back-tracking).
*/
if DOUBLE_COMPARISONS
&& num_dropped_in_row == 0
&& 2 <= write
&& compare(&slice[read], &slice[write - 2]) != Ordering::Less
{
// Quick undo: drop previously accepted element, and overwrite with new one:
dropped.push(slice[write - 1]);
slice[write - 1] = slice[read];
read += 1;
continue;
}
if num_dropped_in_row < RECENCY {
// Drop it:
dropped.push(slice[read]);
read += 1;
num_dropped_in_row += 1;
} else {
/*
We accepted something num_dropped_in_row elements back that made us drop all RECENCY subsequent items.
Accepting that element was obviously a mistake - so let's undo it!
Example problem (RECENCY = 3): 0 1 12 3 4 5 6
0 1 12 is accepted. 3, 4, 5 will be rejected because they are larger than the last kept item (12).
When we get to 5 we reach num_dropped_in_row == RECENCY.
This will trigger an undo where we drop the 12.
When we again go to 3, we will keep it because it is larger than the last kept item (1).
Example worst-case (RECENCY = 3): ...100 101 102 103 104 1 2 3 4 5 ....
100-104 is accepted. When we get to 3 we reach num_dropped_in_row == RECENCY.
We drop 104 and reset the read by RECENCY. We restart, and then we drop again.
This can lead us to backtracking RECENCY number of elements
as many times as the leading non-decreasing subsequence is long.
*/
// Undo dropping the last num_dropped_in_row elements:
let trunc_to_length = dropped.len() - num_dropped_in_row;
dropped.truncate(trunc_to_length);
read -= num_dropped_in_row;
let mut num_backtracked = 1;
write -= 1;
if FAST_BACKTRACKING {
// Back-track until we can accept at least one of the recently dropped elements:
let max_of_dropped = slice[read..(read + num_dropped_in_row + 1)]
.iter()
.max_by(|a, b| compare(a, b))
.unwrap();
while 1 <= write && compare(max_of_dropped, &slice[write - 1]) == Ordering::Less
{
num_backtracked += 1;
write -= 1;
}
}
// Drop the back-tracked elements:
dropped.extend_from_slice(&slice[write..(write + num_backtracked)]);
num_dropped_in_row = 0;
}
}
}
let num_dropped = dropped.len();
// ------------------------------------------------------------------------
// Second step: sort the dropped elements:
dropped.sort_unstable_by(|a, b| compare(a, b));
// ------------------------------------------------------------------------
// Third step: merge slice[..write] and `dropped`:
let mut back = slice.len();
while let Some(&last_dropped) = dropped.last() {
while 0 < write && compare(&last_dropped, &slice[write - 1]) == Ordering::Less {
slice[back - 1] = slice[write - 1];
back -= 1;
write -= 1;
}
slice[back - 1] = last_dropped;
back -= 1;
dropped.pop();
}
num_dropped
}
/// UNSTABLE! FOR INTERNAL USE ONLY.
pub fn sort_copy<T: Copy + Ord>(slice: &mut [T]) -> usize {
sort_copy_by(slice, |a, b| a.cmp(b))
}
// ----------------------------------------------------------------------------
// A note about protecting us from stack unwinding:
//
// If our compare function panics we need to make sure all objects are put back into slice
// so they can be properly destroyed by the caller.
//
// This is done by temporarily bit-copying the data into the dropped vector
// and copying them back if there is a panic.
//
struct DmSorter<'a, T: 'a> {
/// The slice we are sorting
slice: &'a mut [T],
/// Temporary storage of dropped elements.
dropped: Vec<T>,
/// Index in self.slice of where to write the next element to keep.
write: usize,
// slice[write..(write + dropped.len())] is a gap. The elements can be found in dropped
}
impl<'a, T> Drop for DmSorter<'a, T> {
fn drop(&mut self) {
if self.dropped.is_empty() {
return;
}
unsafe {
// This code will only run on stack-unwind (panic).
// Move back all elements into the slice:
ptr::copy_nonoverlapping(
self.dropped.as_ptr(),
self.slice.as_mut_ptr().add(self.write),
self.dropped.len(),
);
// Make sure the objects aren't destroyed when self.dropped is dropped (avoid-double-free).
self.dropped.set_len(0);
}
}
}
#[inline(always)]
unsafe fn unsafe_push<T>(vec: &mut Vec<T>, value: &T) {
let old_len = vec.len();
vec.reserve(1);
ptr::copy_nonoverlapping(value, vec.as_mut_ptr().add(old_len), 1);
vec.set_len(old_len + 1);
}
#[inline(always)]
unsafe fn unsafe_copy<T>(slice: &mut [T], source: usize, dest: usize) {
let ptr = slice.as_mut_ptr();
ptr::copy_nonoverlapping(ptr.add(source), ptr.add(dest), 1);
}
fn sort_move_by<T, F>(slice: &mut [T], mut compare: F)
where
F: FnMut(&T, &T) -> Ordering,
{
unsafe {
if slice.len() < 2 {
return;
}
let mut s = DmSorter {
slice,
dropped: Vec::new(),
write: 0,
};
// ------------------------------------------------------------------------
let mut num_dropped_in_row = 0;
let mut read = 0;
let mut iteration = 0;
let ealy_out_stop = s.slice.len() / EARLY_OUT_TEST_AT;
while read < s.slice.len() {
iteration += 1;
if EARLY_OUT
&& iteration == ealy_out_stop
&& s.dropped.len() as f32 > read as f32 * EARLY_OUT_DISORDER_FRACTION
{
// We have seen a lot of the elements and dropped a lot of them.
// This doesn't look good. Abort.
ptr::copy_nonoverlapping(
s.dropped.as_ptr(),
&mut s.slice[s.write],
s.dropped.len(),
);
s.dropped.set_len(0);
s.slice.sort_unstable_by(|a, b| compare(a, b));
return;
}
if s.write == 0
|| compare(
s.slice.get_unchecked(read),
s.slice.get_unchecked(s.write - 1),
) != Ordering::Less
{
// The element is order - keep it:
if read != s.write {
unsafe_copy(s.slice, read, s.write);
}
read += 1;
s.write += 1;
num_dropped_in_row = 0;
} else {
if DOUBLE_COMPARISONS
&& num_dropped_in_row == 0
&& 2 <= s.write
&& compare(
s.slice.get_unchecked(read),
s.slice.get_unchecked(s.write - 2),
) != Ordering::Less
{
// Quick undo: drop previously accepted element, and overwrite with new one:
unsafe_push(&mut s.dropped, s.slice.get_unchecked(s.write - 1));
unsafe_copy(s.slice, read, s.write - 1);
read += 1;
continue;
}
if num_dropped_in_row < RECENCY {
// Drop it:
unsafe_push(&mut s.dropped, s.slice.get_unchecked(read));
read += 1;
num_dropped_in_row += 1;
} else {
// Undo dropping the last num_dropped_in_row elements:
let trunc_to_length = s.dropped.len() - num_dropped_in_row;
s.dropped.set_len(trunc_to_length);
read -= num_dropped_in_row;
let mut num_backtracked = 1;
s.write -= 1;
if FAST_BACKTRACKING {
// Back-track until we can accept at least one of the recently dropped elements:
let max_of_dropped = s.slice[read..(read + num_dropped_in_row + 1)]
.iter()
.max_by(|a, b| compare(a, b))
.unwrap();
while 1 <= s.write
&& compare(max_of_dropped, s.slice.get_unchecked(s.write - 1))
== Ordering::Less
{
num_backtracked += 1;
s.write -= 1;
}
}
// Append s.slice[read..(read + num_backtracked)] to s.dropped:
{
let old_len = s.dropped.len();
s.dropped.reserve(num_backtracked);
ptr::copy_nonoverlapping(
s.slice.as_ptr().add(s.write),
s.dropped.as_mut_ptr().add(old_len),
num_backtracked,
);
s.dropped.set_len(old_len + num_backtracked);
}
num_dropped_in_row = 0;
}
}
}
// ------------------------------------------------------------------------
s.dropped.sort_unstable_by(|a, b| compare(a, b));
// ------------------------------------------------------------------------
// Merge:
let mut back = s.slice.len();
loop {
let old_len = s.dropped.len();
if old_len == 0 {
break;
}
{
let last_dropped = s.dropped.get_unchecked(old_len - 1);
while 0 < s.write
&& compare(last_dropped, s.slice.get_unchecked(s.write - 1)) == Ordering::Less
{
unsafe_copy(s.slice, s.write - 1, back - 1);
back -= 1;
s.write -= 1;
}
ptr::copy_nonoverlapping(last_dropped, s.slice.get_unchecked_mut(back - 1), 1);
}
back -= 1;
s.dropped.set_len(old_len - 1);
}
}
}
// ----------------------------------------------------------------------------
/// Sorts the elements using the given compare function.
/// # Examples
/// ```
/// let mut numbers : Vec<i32> = vec!(0, 1, 6, 7, 2, 3, 4, 5);
/// dmsort::sort_by(&mut numbers, |a, b| b.cmp(a));
/// assert_eq!(numbers, vec!(7, 6, 5, 4, 3, 2, 1, 0));
/// ```
pub fn sort_by<T, F>(slice: &mut [T], compare: F)
where
F: FnMut(&T, &T) -> Ordering,
{
sort_move_by(slice, compare);
}
/// Sorts the elements using the given key function.
/// # Examples
/// ```
/// let mut numbers : Vec<i32> = vec!(0, 1, 6, 7, 2, 3, 4, 5);
/// dmsort::sort_by_key(&mut numbers, |x| -x);
/// assert_eq!(numbers, vec!(7, 6, 5, 4, 3, 2, 1, 0));
/// ```
pub fn sort_by_key<T, K, F>(slice: &mut [T], mut key: F)
where
K: Ord,
F: FnMut(&T) -> K,
{
sort_by(slice, |a, b| key(a).cmp(&key(b)));
}
/// Sorts the elements using the Ord trait.
/// # Examples
/// ```
/// let mut numbers : Vec<i32> = vec!(0, 1, 6, 7, 2, 3, 4, 5);
/// dmsort::sort(&mut numbers);
/// assert_eq!(numbers, vec!(0, 1, 2, 3, 4, 5, 6, 7));
/// ```
pub fn sort<T: Ord>(slice: &mut [T]) {
sort_move_by(slice, |a, b| a.cmp(b));
}
// ----------------------------------------------------------------------------