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use ahash::{AHasher, RandomState};
use crate::{Entropy, OsEntropy};
#[derive(Clone, Debug)]pub struct RuntimeHasher { inner: RandomState,}
impl RuntimeHasher { pub fn from_entropy(entropy: &dyn Entropy) -> Self { Self { inner: RandomState::with_seeds( entropy.next_u64(), entropy.next_u64(), entropy.next_u64(), entropy.next_u64(), ), } }
pub const fn from_seeds(k0: u64, k1: u64, k2: u64, k3: u64) -> Self { Self { inner: RandomState::with_seeds(k0, k1, k2, k3), } }}
impl Default for RuntimeHasher { fn default() -> Self { Self::from_entropy(&OsEntropy) }}
impl BuildHasher for RuntimeHasher { type Hasher = AHasher;
fn build_hasher(&self) -> Self::Hasher { self.inner.build_hasher() }}
#[cfg(test)]mod tests { use super::*; use crate::OsEntropy; use std::collections::HashMap; use std::sync::Arc; use std::sync::atomic::{AtomicU64, Ordering};
struct CountingEntropy(AtomicU64);
impl Entropy for CountingEntropy { fn next_u64(&self) -> u64 { self.0.fetch_add(1, Ordering::SeqCst) } }
#[test] fn same_seed_inputs_produce_identical_hashes() { let a = RuntimeHasher::from_seeds(1, 2, 3, 4); let b = RuntimeHasher::from_seeds(1, 2, 3, 4); assert_eq!(a.hash_one("limpet"), b.hash_one("limpet")); assert_eq!(a.hash_one(42_u64), b.hash_one(42_u64)); }
#[test] fn different_seeds_produce_different_hashes() { let a = RuntimeHasher::from_seeds(1, 2, 3, 4); let b = RuntimeHasher::from_seeds(5, 6, 7, 8); assert_ne!( a.hash_one("conch"), b.hash_one("conch"), "two seedings must not collapse to the same key state", ); }
#[test] fn from_entropy_consumes_four_words_in_call_order() { let entropy: Arc<dyn Entropy> = Arc::new(CountingEntropy(AtomicU64::new(100))); let hasher = RuntimeHasher::from_entropy(&*entropy); let direct = RuntimeHasher::from_seeds(100, 101, 102, 103); assert_eq!( hasher.hash_one("nautilus"), direct.hash_one("nautilus"), "from_entropy must seed by draining four u64s in order", ); }
#[test] fn os_entropy_seeds_a_usable_hashmap() { let hasher = RuntimeHasher::from_entropy(&OsEntropy); let mut map: HashMap<&str, u32, RuntimeHasher> = HashMap::with_hasher(hasher); map.insert("kelp", 1); map.insert("uni", 2); assert_eq!(map.get("kelp"), Some(&1)); assert_eq!(map.get("uni"), Some(&2)); }}