csf is the Rust library (by Piotr Beling) of (compressed) static functions that use perfect hashing (and value compression).

csf contains the following types that implement static functions: [ls::Map], [fp::Map]. They can represent functions (immutable maps) from a set of (hashable) keys to unsigned integers of given bit-size. They take somewhat more than nb bits to represent a function from an n-element set into a set of b-bit values. The expected time complexities of their construction and evaluation are O(n) and O(1), respectively.

csf contains the following types that implement compressed static functions: [ls::CMap], [fp::CMap], [fp::GOCMap]. They can represent functions (immutable maps) from a set of (hashable) keys to a set of values of any type. To represent a function f:X→Y, they use the space slightly larger than |X|H, where H is the entropy of the distribution of the f values over X. Their expected time complexity is O(c) for evaluation and O(|X|c) for construction (not counting building the encoding dictionary), where c is the average codeword length (given in code fragments) of the values.

None of the static functions (including the compressed ones) included in csf explicitly store keys. Therefore, these functions are usually unable to detect whether an item belongs to the set of keys for which they were constructed. Thus, queried for a value assigned to an item outside that set, they can return any value.

Example

use csf::ls;

let subset: ls::Map = [("alpha", 1u8), ("beta", 0), ("gamma", 1)].as_ref().into();
assert_eq!(subset.get(&"alpha"), 1);
assert_eq!(subset.get(&"beta"), 0);
assert_eq!(subset.get(&"gamma"), 1);
// Any 1-bit value (either 0 or 1) can be returned for other arguments:
assert!(subset.get(&"other") <= 1);