American Flag sort for Rust

The afsort crate implements a sorting algorithm based on American Flag sort. The implementation is currently limited to sort byte slices, e.g. Strings. The main motivation is to sort strings of text, so most of the benchmarks are based on English text strings. When sorting English words, this implementation seems to be about 40% faster than sort_unstable from the Rust standard library.

For small input, this method falls back to the standard library.

Installation

Add the dependency to your Cargo.toml:

[dependencies]
afsort = "0.2"

In your crate root:

extern crate afsort;

Warning: Version 0.1.0 is flawed(slow), use 0.1.1 or later.

Note on upgrading 0.1.x -> 0.2.x: The method afsort::sort_unstable(&mut [AsRef<u8>]) has been removed. Use the af_sort_unstable from the AFSortable trait instead.

Usage

You can now use afsort to e.g. sort arrays of strings or string slices.

use afsort::AFSortable;
let mut strings = vec!("red", "green", "blue");
strings.af_sort_unstable();
assert_eq!(strings, vec!["blue", "green", "red"]);

It also works on u8, u16, u32 and u64:

use afsort::AFSortable;
let mut strings = vec!(1u32, 2u32, 7u32);
strings.af_sort_unstable();
assert_eq!(strings, vec![1u32, 2u32, 7u32]);

You can also sort by an extractor function, e.g.:

use afsort;
let mut tuples = vec![("b", 2), ("a", 1)];
afsort::sort_unstable_by(&mut tuples, |t| &t.0);
assert_eq!(tuples, vec![("a", 1), ("b", 2)]);

The af_sort_unstable() method is implemented for all slices of values that implement the afsort::DigitAt and the Ord traits. The DigitAt trait is implemented for &str , String, [u8], u8, u16, u32 and u64. All of these also implement Ord. You can also implement this trait for any other type.

Motivation

Essentially, I noticed that sorting of strings took a long time when using the fst crate, since it requires the input to be ordered. Since sorting strings is a general problem, this is now a crate.

Performance

As mentioned, this implementation seems to be about 40% faster than the sort in the standard library, when sorting strings of random English words. It is slower for strings that are already sorted. The implementation is fairly naive, so I would not be surprised if it could be improved further.

For numbers, it currently seems to be slower than the standard library. I suspect this is due to more swaps happening in afsort than in the standard library. I want to fix this.

This will be heavily affected by the distribution of values in the input though. As always with performance: your milage may vary. Profile your usage.

You can run the benchmark tests using cargo bench (currently requires nightly rust), like this:

% cargo bench
    Finished release [optimized] target(s) in 0.0 secs
     Running target/release/deps/afsort-2f0d4e495216be99
running 10 tests
test tests::correct_radix_for_u16 ... ignored
test tests::correct_radix_for_u32 ... ignored
test tests::correct_radix_for_u64 ... ignored
test tests::correct_radix_for_u8 ... ignored
test tests::sorts_strings_same_as_unstable ... ignored
test tests::sorts_tuples_same_as_unstable ... ignored
test tests::sorts_u16_same_as_unstable ... ignored
test tests::sorts_u32_same_as_unstable ... ignored
test tests::sorts_u64_same_as_unstable ... ignored
test tests::sorts_u8_same_as_unstable ... ignored
test result: ok. 0 passed; 0 failed; 10 ignored; 0 measured; 0 filtered out
     Running target/release/deps/bench-42a0c77149fb906a
running 16 tests
test sort_en_strings_lower_10_000_af   ... bench:   1,881,300 ns/iter (+/- 618,858)
test sort_en_strings_lower_10_000_std  ... bench:   2,594,388 ns/iter (+/- 767,774)
test sort_en_strings_rand_100_000_af   ... bench:  23,101,465 ns/iter (+/- 12,052,025)
test sort_en_strings_rand_100_000_std  ... bench:  31,536,516 ns/iter (+/- 12,910,887)
test sort_en_strings_rand_10_000_af    ... bench:   1,588,372 ns/iter (+/- 568,509)
test sort_en_strings_rand_10_000_std   ... bench:   2,193,132 ns/iter (+/- 648,297)
test sort_en_strings_sorted_10_000_af  ... bench:     806,419 ns/iter (+/- 128,186)
test sort_en_strings_sorted_10_000_std ... bench:     589,161 ns/iter (+/- 340,707)
test sort_u16_1_000_000_af             ... bench:  19,442,855 ns/iter (+/- 1,642,992)
test sort_u16_1_000_000_std            ... bench:  21,401,736