sudachi/util/fxhash.rs
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/*
* Copyright (c) 2021 Works Applications Co., Ltd.
*
* 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
*
* 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.
*/
// Adopted from: https://github.com/cbreeden/fxhash/blob/master/lib.rs
// Removed functionality that were useless for us
// Original Copyright:
// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
//! # Fx Hash
//!
//! This hashing algorithm was extracted from the Rustc compiler. This is the same hashing
//! algorithm used for some internal operations in Firefox. The strength of this algorithm
//! is in hashing 8 bytes at a time on 64-bit platforms, where the FNV algorithm works on one
//! byte at a time.
//!
//! ## Disclaimer
//!
//! It is **not a cryptographically secure** hash, so it is strongly recommended that you do
//! not use this hash for cryptographic purproses. Furthermore, this hashing algorithm was
//! not designed to prevent any attacks for determining collisions which could be used to
//! potentially cause quadratic behavior in `HashMap`s. So it is not recommended to expose
//! this hash in places where collissions or DDOS attacks may be a concern.
use std::convert::TryInto;
use std::default::Default;
use std::hash::{BuildHasherDefault, Hasher};
use std::ops::BitXor;
/// A builder for default Fx hashers.
pub type FxBuildHasher = BuildHasherDefault<FxHasher64>;
const ROTATE: u32 = 5;
const SEED64: u64 = 0x51_7c_c1_b7_27_22_0a_95;
const SEED32: u32 = 0x9e_37_79_b9;
#[cfg(target_pointer_width = "64")]
const SEED: usize = SEED64 as usize;
trait HashWord {
fn hash_word(&mut self, _: Self);
}
macro_rules! impl_hash_word {
($($ty:ty = $key:ident),* $(,)*) => (
$(
impl HashWord for $ty {
#[inline(always)]
fn hash_word(&mut self, word: Self) {
*self = self.rotate_left(ROTATE).bitxor(word).wrapping_mul($key);
}
}
)*
)
}
impl_hash_word!(usize = SEED, u32 = SEED32, u64 = SEED64);
#[inline]
fn write64(mut hash: u64, mut bytes: &[u8]) -> u64 {
while bytes.len() >= 8 {
let (data, rem) = bytes.split_at(8);
hash.hash_word(u64::from_ne_bytes(data.try_into().unwrap()));
bytes = rem;
}
if bytes.len() >= 4 {
let (data, rem) = bytes.split_at(4);
hash.hash_word(u32::from_ne_bytes(data.try_into().unwrap()) as u64);
bytes = rem;
}
if bytes.len() >= 2 {
let (data, rem) = bytes.split_at(2);
hash.hash_word(u16::from_ne_bytes(data.try_into().unwrap()) as u64);
bytes = rem;
}
if let Some(&byte) = bytes.first() {
hash.hash_word(u64::from(byte));
}
hash
}
/// This hashing algorithm was extracted from the Rustc compiler.
/// This is the same hashing algorithm used for some internal operations in Firefox.
/// The strength of this algorithm is in hashing 8 bytes at a time on any platform,
/// where the FNV algorithm works on one byte at a time.
///
/// This hashing algorithm should not be used for cryptographic, or in scenarios where
/// DOS attacks are a concern.
#[derive(Debug, Clone)]
pub struct FxHasher64 {
hash: u64,
}
impl Default for FxHasher64 {
#[inline]
fn default() -> FxHasher64 {
FxHasher64 { hash: 0 }
}
}
impl Hasher for FxHasher64 {
#[inline]
fn finish(&self) -> u64 {
self.hash
}
#[inline]
fn write(&mut self, bytes: &[u8]) {
self.hash = write64(self.hash, bytes);
}
#[inline]
fn write_u8(&mut self, i: u8) {
self.hash.hash_word(u64::from(i));
}
#[inline]
fn write_u16(&mut self, i: u16) {
self.hash.hash_word(u64::from(i));
}
#[inline]
fn write_u32(&mut self, i: u32) {
self.hash.hash_word(u64::from(i));
}
#[inline]
fn write_u64(&mut self, i: u64) {
self.hash.hash_word(i);
}
#[inline]
fn write_usize(&mut self, i: usize) {
self.hash.hash_word(i as u64);
}
}