gecko-dev/third_party/rust/pdqsort
Manish Goregaokar cd6c97ea60 Bug 1336607 - Update vendored Rust sources to include geckolib dependencies; r=froydnj
MozReview-Commit-ID: BOgu41N351y

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..
benches
src
.cargo-checksum.json
.cargo-ok
.gitignore
.travis.yml
Cargo.toml
LICENSE-APACHE
LICENSE-MIT
README.md

Pattern-defeating quicksort

Build Status License Cargo Documentation

This sort is significantly faster than the standard sort in Rust. In particular, it sorts random arrays of integers approximately 40% faster. The key drawback is that it is an unstable sort (i.e. may reorder equal elements). However, in most cases stability doesn't matter anyway.

The algorithm was designed by Orson Peters and first published at: https://github.com/orlp/pdqsort

Properties

  • Best-case running time is O(n).
  • Worst-case running time is O(n log n).
  • Unstable, i.e. may reorder equal elements.
  • Does not allocate additional memory.
  • Uses #![no_std].

Examples

extern crate pdqsort;

let mut v = [-5i32, 4, 1, -3, 2];

pdqsort::sort(&mut v);
assert!(v == [-5, -3, 1, 2, 4]);

pdqsort::sort_by(&mut v, |a, b| b.cmp(a));
assert!(v == [4, 2, 1, -3, -5]);

pdqsort::sort_by_key(&mut v, |k| k.abs());
assert!(v == [1, 2, -3, 4, -5]);

A simple benchmark

Sorting 10 million random numbers of type u64:

Sort Time
pdqsort 396 ms
slice::sort 668 ms
quickersort 777 ms
dmsort 728 ms
rdxsort 602 ms

Extensive benchmarks

The benchmarks that follow are used in Rust for testing the performance of slice::sort.

Benchmark pdqsort slice::sort quickersort dmsort rdxsort
large_ascending 11 us 9 us 12 us 22 us 358 us
large_descending 14 us 14 us 46 us 144 us 347 us
large_random 342 us 509 us 534 us 544 us 399 us
large_random_expensive 63 ms 24 ms - 31 ms -
large_mostly_ascending 82 us 239 us 129 us 45 us 353 us
large_mostly_descending 93 us 267 us 135 us 282 us 349 us
large_big_ascending 375 us 370 us 374 us 412 us 49,597 us
large_big_descending 441 us 441 us 571 us 814 us 49,675 us
large_big_random 1,573 us 2,141 us 1,971 us 2,308 us 43,578 us
medium_ascending 186 ns 145 ns 148 ns 259 ns 4,509 ns
medium_descending 214 ns 188 ns 490 ns 1,344 ns 4,947 ns
medium_random 2,926 ns 3,297 ns 3,252 ns 3,722 ns 6,466 ns
small_ascending 32 ns 32 ns 25 ns 47 ns 1,597 ns
small_descending 55 ns 55 ns 51 ns 232 ns 1,595 ns
small_random 347 ns 346 ns 333 ns 484 ns 3,841 ns
small_big_ascending 92 ns 92 ns 89 ns 136 ns 35,749 ns
small_big_descending 246 ns 246 ns 420 ns 517 ns 35,807 ns
small_big_random 492 ns 492 ns 582 ns 671 ns 46,393 ns