Struct BlackrockPermutation 

pub struct BlackrockPermutation { /* private fields */ }

A Feistel-network-based permutation over [0, range).

Maps each index to a unique pseudorandom output in the same range. Used to randomize scan order without storing the full permutation in memory.

Implementations

impl BlackrockPermutation

pub fn new(range: u64, seed: u64) -> Self

Create a new permutation over [0, range) with the given seed.

Panics

Panics if range is 0.

pub fn shuffle(&self, index: u64) -> u64

Permute index i to its randomized output.

If the output falls outside [0, range) (due to the Feistel network operating on the next power-of-two), we “cycle walk” until we land inside the valid range.

pub fn unshuffle(&self, permuted: u64) -> u64

Inverse permutation: given an output, recover the original index.