Add FxHasher, a faster alternative to FnvHasher.
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src/librustc_data_structures/fx.rs
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115
src/librustc_data_structures/fx.rs
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// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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use std::collections::{HashMap, HashSet};
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use std::default::Default;
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use std::hash::{Hasher, Hash, BuildHasherDefault};
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use std::ops::BitXor;
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pub type FxHashMap<K, V> = HashMap<K, V, BuildHasherDefault<FxHasher>>;
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pub type FxHashSet<V> = HashSet<V, BuildHasherDefault<FxHasher>>;
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#[allow(non_snake_case)]
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pub fn FxHashMap<K: Hash + Eq, V>() -> FxHashMap<K, V> {
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HashMap::default()
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}
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#[allow(non_snake_case)]
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pub fn FxHashSet<V: Hash + Eq>() -> FxHashSet<V> {
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HashSet::default()
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}
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/// A speedy hash algorithm for use within rustc. The hashmap in libcollections
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/// by default uses SipHash which isn't quite as speedy as we want. In the
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/// compiler we're not really worried about DOS attempts, so we use a fast
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/// non-cryptographic hash.
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///
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/// This is the same as the algorithm used by Firefox -- which is a homespun
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/// one not based on any widely-known algorithm -- though modified to produce
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/// 64-bit hash values instead of 32-bit hash values. It consistently
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/// out-performs an FNV-based hash within rustc itself -- the collision rate is
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/// similar or slightly worse than FNV, but the speed of the hash function
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/// itself is much higher because it works on up to 8 bytes at a time.
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pub struct FxHasher {
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hash: usize
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}
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#[cfg(target_pointer_width = "32")]
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const K: usize = 0x9e3779b9;
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#[cfg(target_pointer_width = "64")]
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const K: usize = 0x517cc1b727220a95;
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impl Default for FxHasher {
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#[inline]
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fn default() -> FxHasher {
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FxHasher { hash: 0 }
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}
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}
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impl FxHasher {
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#[inline]
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fn add_to_hash(&mut self, i: usize) {
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self.hash = self.hash.rotate_left(5).bitxor(i).wrapping_mul(K);
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}
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}
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impl Hasher for FxHasher {
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#[inline]
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fn write(&mut self, bytes: &[u8]) {
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for byte in bytes {
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let i = *byte;
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self.add_to_hash(i as usize);
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}
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}
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#[inline]
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fn write_u8(&mut self, i: u8) {
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self.add_to_hash(i as usize);
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}
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#[inline]
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fn write_u16(&mut self, i: u16) {
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self.add_to_hash(i as usize);
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}
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#[inline]
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fn write_u32(&mut self, i: u32) {
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self.add_to_hash(i as usize);
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}
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#[cfg(target_pointer_width = "32")]
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#[inline]
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fn write_u64(&mut self, i: u64) {
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self.add_to_hash(i as usize);
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self.add_to_hash((i >> 32) as usize);
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}
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#[cfg(target_pointer_width = "64")]
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#[inline]
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fn write_u64(&mut self, i: u64) {
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self.add_to_hash(i as usize);
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}
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#[inline]
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fn write_usize(&mut self, i: usize) {
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self.add_to_hash(i);
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}
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#[inline]
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fn finish(&self) -> u64 {
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self.hash as u64
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}
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}
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pub fn hash<T: Hash>(v: &T) -> u64 {
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let mut state = FxHasher::default();
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v.hash(&mut state);
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state.finish()
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}
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