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interner.rs
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interner.rs
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// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements. See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership. The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License. You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied. See the License for the
// specific language governing permissions and limitations
// under the License.
use crate::data_type::AsBytes;
use hashbrown::hash_map::RawEntryMut;
use hashbrown::HashMap;
use std::hash::Hash;
const DEFAULT_DEDUP_CAPACITY: usize = 4096;
/// Storage trait for [`Interner`]
pub trait Storage {
type Key: Copy;
type Value: AsBytes + PartialEq + ?Sized;
/// Gets an element by its key
fn get(&self, idx: Self::Key) -> &Self::Value;
/// Adds a new element, returning the key
fn push(&mut self, value: &Self::Value) -> Self::Key;
}
/// A generic value interner supporting various different [`Storage`]
#[derive(Debug, Default)]
pub struct Interner<S: Storage> {
state: ahash::RandomState,
/// Used to provide a lookup from value to unique value
///
/// Note: `S::Key`'s hash implementation is not used, instead the raw entry
/// API is used to store keys w.r.t the hash of the strings themselves
///
dedup: HashMap<S::Key, (), ()>,
storage: S,
}
impl<S: Storage> Interner<S> {
/// Create a new `Interner` with the provided storage
pub fn new(storage: S) -> Self {
Self {
state: Default::default(),
dedup: HashMap::with_capacity_and_hasher(DEFAULT_DEDUP_CAPACITY, ()),
storage,
}
}
/// Intern the value, returning the interned key, and if this was a new value
pub fn intern(&mut self, value: &S::Value) -> S::Key {
let hash = compute_hash(&self.state, value);
let entry = self
.dedup
.raw_entry_mut()
.from_hash(hash, |index| value == self.storage.get(*index));
match entry {
RawEntryMut::Occupied(entry) => *entry.into_key(),
RawEntryMut::Vacant(entry) => {
let key = self.storage.push(value);
*entry
.insert_with_hasher(hash, key, (), |key| {
compute_hash(&self.state, self.storage.get(*key))
})
.0
}
}
}
/// Returns the storage for this interner
pub fn storage(&self) -> &S {
&self.storage
}
/// Unwraps the inner storage
pub fn into_inner(self) -> S {
self.storage
}
}
fn compute_hash<T: AsBytes + ?Sized>(state: &ahash::RandomState, value: &T) -> u64 {
use std::hash::{BuildHasher, Hasher};
let mut hasher = state.build_hasher();
value.as_bytes().hash(&mut hasher);
hasher.finish()
}