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Introsort
This is an implementation of the introsort sorting algorithm.
This crate does not depend on std
, and can be used with #![no_std]
crates.
It does however depend on core
, but has no other dependencies except for testing.
To use with cargo, add the following to your Cargo.toml
:
[]
= "0.4.0"
and in your crate root, add
extern crate introsort;
Interface
The interface is similar to the standard library sort
and sort_by
functions.
An example:
extern crate introsort;
Unlike the standard library sort function, introsort is not a stable sort.
Details
At its heart, it is a dual-pivot quicksort. For partition with many equal elements, it will instead use a single-pivot quicksort optimized for this case. It detects excessive recursion during quicksort and switches to heapsort if need be, guaranteeing O(n log(n)) runtime on all inputs. For small partitions it uses insertion sort instead of quicksort.
Unlike the std
sort, it does not allocate.
Performance
It is quite fast, outperforming the standard sort on all data sets I have tried.
The performance difference varies depending on the characteristics of the data.
On large, completely random arrays, introsort
is only 5-10% faster than the standard sort.
However, introsort
's performance is greatly improved if the data has few unique values or is (partially) sorted (including reversed data).
For sorted data, introsort
is ~4-5 times faster, and for data with few unique values it can be more than 20 times faster.
Detailed benchmark data (only for integers as of now) is available.
Floating point
The crate, is built with the "float" feature (which is the default), also includes a sort_floats
function.
Floating point numbers are not Ord
, only PartialOrd
, so sort
can not be used on them.
The ordering used by sort_floats
is
| -inf | < 0 | -0 | +0 | > 0 | +inf | NaN |
sort_floats
is much more efficient than passing a comparator function implementing this ordering to sort_by
.