permutation_compression
A Rust library to compress permutations.
// create a random permutation by shuffling
let mut rng = rand::thread_rng();
let mut data: Vec<u32> = (0..1_000_000_u32).collect();
data.shuffle(&mut rng);
let orig_perm = data.clone();
// compress the permutation
let compressed = compress_permutation(CompressionMode::Slow, data);
// recover the compressed permutation
let recovered = decompress_permutation(CompressionMode::Slow, &compressed);
assert_eq!(recovered, orig_perm);The information-theoretic lower bound for compressing a permutation of size n is O(log2(n!)). In fast mode, we achieve O(n log n) compression using bitpacking. In slow mode, we remove another O(n).
On my personal hardware:
| mode | n | compression time | decompression time | uncompressed size | compressed size | compression ratio |
|---|---|---|---|---|---|---|
| Fast | 1M | < 5ms | < 5ms | 4MB | 2.5MB | 1.595 |
| Slow | 1M | 220ms | 185ms | 4MB | 2.4MB | 1.684 |
This code is available under the AGPL-3.0 license. See COPYING for more information.