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// 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.
#![deny(missing_docs)]
//! # Fx Hash
//!
//! This hashing algorithm was extracted from the Rustc compiler. This is the same hashing
//! algoirthm 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::collections::{HashMap, HashSet};
use std::default::Default;
use std::hash::{Hasher, Hash, BuildHasherDefault};
use std::ops::BitXor;
extern crate byteorder;
use byteorder::{ByteOrder, NativeEndian};
/// A builder for default Fx hashers.
pub type FxBuildHasher = BuildHasherDefault<FxHasher>;
/// A `HashMap` using a default Fx hasher.
pub type FxHashMap<K, V> = HashMap<K, V, FxBuildHasher>;
/// A `HashSet` using a default Fx hasher.
pub type FxHashSet<V> = HashSet<V, FxBuildHasher>;
const ROTATE: u32 = 5;
const SEED64: u64 = 0x517cc1b727220a95;
const SEED32: u32 = (SEED64 & 0xFFFF_FFFF) as u32;
#[cfg(target_pointer_width = "32")]
const SEED: usize = SEED32 as usize;
#[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 $ty {
#[inline]
fn hash_word(&mut self, word: Self) {
*self = self.rotate_left(ROTATE).bitxor(word).wrapping_mul($key);
)*
)
impl_hash_word!(usize = SEED, u32 = SEED32, u64 = SEED64);
fn write32(mut hash: u32, mut bytes: &[u8]) -> u32 {
while bytes.len() >= 4 {
let n = NativeEndian::read_u32(bytes);
hash.hash_word(n);
bytes = bytes.split_at(4).1;
for byte in bytes {
hash.hash_word(*byte as u32);
hash
fn write64(mut hash: u64, mut bytes: &[u8]) -> u64 {
while bytes.len() >= 8 {
let n = NativeEndian::read_u64(bytes);
bytes = bytes.split_at(8).1;
if bytes.len() >= 4 {
hash.hash_word(n as u64);
hash.hash_word(*byte as u64);
fn write(hash: usize, bytes: &[u8]) -> usize {
write32(hash as u32, bytes) as usize
write64(hash as u64, bytes) as usize
/// This hashing algorithm was extracted from the Rustc compiler.
/// This is the same hashing algoirthm 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.
///
/// This hashing algorithm should not be used for cryptographic, or in scenarios where
/// DOS attacks are a concern.
#[derive(Debug, Clone)]
pub struct FxHasher {
hash: usize,
impl Default for FxHasher {
fn default() -> FxHasher {
FxHasher { hash: 0 }
impl Hasher for FxHasher {
fn write(&mut self, bytes: &[u8]) {
self.hash = write(self.hash, bytes);
fn write_u8(&mut self, i: u8) {
self.hash.hash_word(i as usize);
fn write_u16(&mut self, i: u16) {
fn write_u32(&mut self, i: u32) {
fn write_u64(&mut self, i: u64) {
self.hash.hash_word((i >> 32) as usize);
fn write_usize(&mut self, i: usize) {
self.hash.hash_word(i);
fn finish(&self) -> u64 {
self.hash as u64
/// The strength of this algorithm is in hashing 8 bytes at a time on any platform,
pub struct FxHasher64 {
hash: u64,
impl Default for FxHasher64 {
fn default() -> FxHasher64 {
FxHasher64 { hash: 0 }
impl Hasher for FxHasher64 {
self.hash = write64(self.hash, bytes);
self.hash.hash_word(i as u64);
self.hash
/// The strength of this algorithm is in hashing 4 bytes at a time on any platform,
pub struct FxHasher32 {
hash: u32,
impl Default for FxHasher32 {
fn default() -> FxHasher32 {
FxHasher32 { hash: 0 }
impl Hasher for FxHasher32 {
self.hash = write32(self.hash, bytes);
self.hash.hash_word(i as u32);
self.hash.hash_word((i >> 32) as u32);
self.write_u32(i as u32);
self.write_u64(i as u64);
/// A convenience function for when you need a quick 64-bit hash.
pub fn hash64<T: Hash + ?Sized>(v: &T) -> u64 {
let mut state = FxHasher64::default();
v.hash(&mut state);
state.finish()
/// A convenience function for when you need a quick 32-bit hash.
pub fn hash32<T: Hash + ?Sized>(v: &T) -> u32 {
let mut state = FxHasher32::default();
state.finish() as u32
/// A convenience function for when you need a quick usize hash.
pub fn hash<T: Hash + ?Sized>(v: &T) -> usize {
let mut state = FxHasher::default();
state.finish() as usize