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/*
* Copyright 2019 The Starlark in Rust Authors.
* Copyright (c) Facebook, Inc. and its affiliates.
*
* Licensed 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
*
* https://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 std::hash::BuildHasher;
use std::hash::Hasher;
use dupe::Dupe;
use fxhash::FxHasher64;
use crate::hash_value::StarlarkHashValue;
/// A hasher used by Starlark implementation.
///
/// Starlark relies on stable hashing, and this is the hasher.
#[derive(Default)]
pub struct StarlarkHasher(
// TODO(nga): `FxHasher64` is endian-dependent, this is not right.
FxHasher64,
);
impl StarlarkHasher {
/// Creates a new hasher.
#[inline]
pub fn new() -> StarlarkHasher {
StarlarkHasher::default()
}
/// Finish the hash computation and return the result.
#[inline]
pub fn finish_small(self) -> StarlarkHashValue {
// NOTE: Here we throw away half the key material we are given,
// taking only the lower 32 bits.
// Not a problem because `DefaultHasher` produces well-swizzled bits.
StarlarkHashValue::new_unchecked(self.finish() as u32)
}
}
impl Hasher for StarlarkHasher {
#[inline]
fn finish(&self) -> u64 {
self.0.finish()
}
#[inline]
fn write(&mut self, bytes: &[u8]) {
self.0.write(bytes)
}
}
/// [`BuildHasher`] implementation which produces [`StarlarkHasher`].
#[derive(Default, Debug, Clone, Copy, Dupe)]
pub struct StarlarkHasherBuilder;
impl BuildHasher for StarlarkHasherBuilder {
type Hasher = StarlarkHasher;
#[inline]
fn build_hasher(&self) -> StarlarkHasher {
StarlarkHasher::default()
}
}