ph is the Rust library (by Piotr Beling) of data structures based on perfect hashing.

The library contains an implementation of two variants of the fingerprint-based minimal perfect hash function without (FMPH, [fmph::Function]) and with (FMPHGO, [fmph::GOFunction]) group optimization. A minimal perfect hash function (MPHF) is a bijection from a key set K to the set {0, 1, ..., |K|−1}.

FMPH and FMPHGO can be constructed for any set K (given in advance) of hashable items and represented using about 2.8 and 2.1 bits per key (regardless of key types), respectively. FMPH and FMPHGO are fast (O(1)) to evaluate. Their construction requires very little auxiliary memory, takes a short (O(|K|)) time (which is especially true for FMPH) and, in addition, can be parallelized.

Bibliography

When using ph for research purposes, please cite the following paper which provides details on FMPH and FMPHGO:

• Piotr Beling, Fingerprinting-based minimal perfect hashing revisited, ACM Journal of Experimental Algorithmics, 2023, https://doi.org/10.1145/3596453

Example

use ph::fmph;

let keys = ['a', 'b', 'z'];
let f = fmph::Function::from(&keys[..]);
// f assigns each key a unique number from the set {0, 1, 2}
for k in keys { println!("The key {} is assigned the value {}.", k, f.get(&k).unwrap()); }
let mut values = [f.get(&'a').unwrap(), f.get(&'b').unwrap(), f.get(&'z').unwrap()];
values.sort();
assert_eq!(values, [0, 1, 2]);