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Make it possible to create a ConsistentPermutation of zero elements #167

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Merged
bb8gh merged 1 commit into from
Oct 7, 2026
Merged

Make it possible to create a ConsistentPermutation of zero elements #167

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2 changes: 1 addition & 1 deletion crates/consistent-choose-k/Cargo.toml
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Original file line number Diff line number Diff line change
@@ -1,6 +1,6 @@
[package]
name = "consistent-choose-k"
version = "0.1.1"
version = "0.1.2"
edition = "2021"
description = "Stateless consistent choose-k hashing for replication, failover, and bounded-load placement."
repository = "https://github.com/github/rust-gems"
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8 changes: 5 additions & 3 deletions crates/consistent-choose-k/src/consistent_permutation.rs
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Expand Up @@ -144,7 +144,7 @@ impl ConsistentPermutation {
/// automatically by [`rounds_for_n_bits`] given that layer's bit
/// width.
///
/// `n` must satisfy `1 <= n <= 2^30`.
/// `n` must satisfy `n <= 2^30`.
///
/// `master_key` is used directly as the Feistel key — the
/// constructor does **not** avalanche it. Pass a high-entropy
Expand All @@ -153,7 +153,6 @@ impl ConsistentPermutation {
/// low-entropy keys will produce visibly correlated permutations
/// across consecutive iterators.
pub fn new(n: u32, master_key: u64) -> Self {
assert!(n > 0, "n must be at least 1");
assert!(n <= 1u32 << 30, "n must be at most 2^30");
// Smallest `j_max` such that `4^(j_max + 1) >= n`. For
// `n >= 2`, `(n-1).ilog2() = ceil(log2(n)) - 1`, so dividing
Expand All @@ -178,6 +177,9 @@ impl Iterator for ConsistentPermutation {
type Item = u32;

fn next(&mut self) -> Option<u32> {
if self.n == 0 {
return None;
}
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let num_layers = self.counters.len();
let j_max = (num_layers - 1) as u32;
let n = self.n;
Expand Down Expand Up @@ -285,7 +287,7 @@ mod tests {
#[test]
fn no_duplicates_within_universe() {
for seed in 0..32u64 {
for n in [1u32, 2, 3, 4, 5, 7, 8, 9, 16, 17, 31, 32, 33, 100, 1000] {
for n in [0u32, 1, 2, 3, 4, 5, 7, 8, 9, 16, 17, 31, 32, 33, 100, 1000] {
let iter = ConsistentPermutation::new(n, 0x9E37_79B9_7F4A_7C15 ^ seed);
let emitted: Vec<u32> = iter.collect();
assert_eq!(
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