Crate smallperm 

smallperm

High-performance pseudo-random permutations using Feistel networks.

This library provides O(1) memory and O(1) expected time per element for generating pseudo-random permutations, making it ideal for shuffling large datasets in machine learning contexts where time-to-first-sample and memory overhead are critical.

Features

• O(1) memory: No need to store the entire permutation
• O(1) random access: Get any element of the permutation instantly
• Invertible: Map both forward and backward between indices and values
• Deterministic: Same seed produces same permutation across runs
• Supports up to 2^128 elements

Example

use smallperm::Permutation;

// Create a permutation of 1000 elements with seed 42
let perm = Permutation::new(1000, 42);

// Iterate through the permutation
for (i, value) in perm.iter().enumerate().take(10) {
    println!("perm[{}] = {}", i, value);
}

// Random access
let value = perm.get(500).unwrap();
println!("perm[500] = {}", value);

// Inverse lookup
let index = perm.index_of(value).unwrap();
assert_eq!(index, 500);

Structs

FeistelNetwork

Implements a Feistel network, which can take a non-invertible pseudo-random function (PRF) and turn it into an invertible pseudo-random permutation (PRP).

Permutation

A pseudo-random permutation with O(1) memory and O(1) access time.

PermutationIter

Iterator over a permutation.

Permutor

Functions

sample

Sample k unique random elements from a slice.

sample_indices

Sample k unique random indices from [0, n).

shuffle

Shuffle a slice and return a new Vec with the shuffled elements.

shuffle_in_place

Shuffle a mutable slice in place.