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//! # aHash //! //! This hashing algorithm is intended to be a high performance, (hardware specific), keyed hash function. //! This can be seen as a DOS resistant alternative to `FxHash`, or a fast equivalent to `SipHash`. //! It provides a high speed hash algorithm, but where the result is not predictable without knowing a Key. //! This allows it to be used in a `HashMap` without allowing for the possibility that an malicious user can //! induce a collision. //! //! # How aHash works //! //! aHash uses the hardware AES instruction on x86 processors to provide a keyed hash function. //! It uses two rounds of AES per hash. So it should not be considered cryptographically secure. #![deny(clippy::correctness, clippy::complexity, clippy::perf)] #![allow(clippy::pedantic, clippy::cast_lossless, clippy::unreadable_literal)] #![cfg_attr(all(not(test), not(feature = "std")), no_std)] extern crate const_random; #[macro_use] mod convert; #[cfg(all(any(target_arch = "x86", target_arch = "x86_64"), target_feature = "aes"))] mod aes_hash; mod fallback_hash; #[cfg(test)] mod hash_quality_test; #[cfg(feature = "std")] mod hash_map; #[cfg(feature = "std")] mod hash_set; #[cfg(feature = "compile-time-rng")] use const_random::const_random; use core::hash::BuildHasher; use core::sync::atomic::AtomicUsize; use core::sync::atomic::Ordering; #[cfg(all(any(target_arch = "x86", target_arch = "x86_64"), target_feature = "aes"))] pub use crate::aes_hash::AHasher; #[cfg(not(all(any(target_arch = "x86", target_arch = "x86_64"), target_feature = "aes")))] pub use crate::fallback_hash::AHasher; #[cfg(feature = "std")] pub use crate::hash_map::AHashMap; #[cfg(feature = "std")] pub use crate::hash_set::AHashSet; ///This constant come from Kunth's prng const MULTIPLE: u64 = 6364136223846793005; // Const random provides randomized starting key with no runtime cost. #[cfg(feature = "compile-time-rng")] static SEED: AtomicUsize = AtomicUsize::new(const_random!(u64)); #[cfg(not(feature = "compile-time-rng"))] static SEED: AtomicUsize = AtomicUsize::new(MULTIPLE as usize); /// Provides a default [Hasher] compile time generated constants for keys. /// This is typically used in conjunction with [`BuildHasherDefault`] to create /// [AHasher]s in order to hash the keys of the map. /// /// # Example /// ``` /// use std::hash::BuildHasherDefault; /// use ahash::{AHasher, ABuildHasher}; /// use std::collections::HashMap; /// /// let mut map: HashMap<i32, i32, ABuildHasher> = HashMap::default(); /// map.insert(12, 34); /// ``` /// /// [BuildHasherDefault]: std::hash::BuildHasherDefault /// [Hasher]: std::hash::Hasher /// [HashMap]: std::collections::HashMap #[cfg(feature = "compile-time-rng")] impl Default for AHasher { /// Constructs a new [AHasher] with compile time generated constants for keys. /// This means the keys will be the same from one instance to another, /// but different from build to the next. So if it is possible for a potential /// attacker to have access to the compiled binary it would be better /// to specify keys generated at runtime. /// /// This is defined only if the `compile-time-rng` feature is enabled. /// /// # Examples /// /// ``` /// use ahash::AHasher; /// use std::hash::Hasher; /// /// let mut hasher_1 = AHasher::default(); /// let mut hasher_2 = AHasher::default(); /// /// hasher_1.write_u32(1234); /// hasher_2.write_u32(1234); /// /// assert_eq!(hasher_1.finish(), hasher_2.finish()); /// ``` #[inline] fn default() -> AHasher { AHasher::new_with_keys(const_random!(u64), const_random!(u64)) } } /// Provides a [Hasher] factory. This is typically used (e.g. by [`HashMap`]) to create /// [AHasher]s in order to hash the keys of the map. See `build_hasher` below. /// /// [build_hasher]: ahash:: /// [Hasher]: std::hash::Hasher /// [BuildHasher]: std::hash::BuildHasher /// [HashMap]: std::collections::HashMap #[derive(Clone)] pub struct ABuildHasher { k0: u64, k1: u64, } impl ABuildHasher { #[inline] pub fn new() -> ABuildHasher { //Using a self pointer. When running with ASLR this is a random value. let previous = SEED.load(Ordering::Relaxed) as u64; let stack_mem_loc = &previous as *const _ as u64; //This is similar to the update function in the fallback. //only one multiply is needed because memory locations are not under an attackers control. let current_seed = previous.wrapping_mul(MULTIPLE).wrapping_add(stack_mem_loc).rotate_left(31); SEED.store(current_seed as usize, Ordering::Relaxed); ABuildHasher { k0: &SEED as *const _ as u64, k1: current_seed } } } impl Default for ABuildHasher { #[inline] fn default() -> Self { Self::new() } } impl BuildHasher for ABuildHasher { type Hasher = AHasher; /// Constructs a new [AHasher] with keys based on compile time generated constants** and the location /// of the this object in memory. This means that two different [BuildHasher]s will will generate /// [AHasher]s that will return different hashcodes, but [Hasher]s created from the same [BuildHasher] /// will generate the same hashes for the same input data. /// /// ** - only if the `compile-time-rng` feature is enabled. /// /// # Examples /// /// ``` /// use ahash::{AHasher, ABuildHasher}; /// use std::hash::{Hasher, BuildHasher}; /// /// let build_hasher = ABuildHasher::new(); /// let mut hasher_1 = build_hasher.build_hasher(); /// let mut hasher_2 = build_hasher.build_hasher(); /// /// hasher_1.write_u32(1234); /// hasher_2.write_u32(1234); /// /// assert_eq!(hasher_1.finish(), hasher_2.finish()); /// /// let other_build_hasher = ABuildHasher::new(); /// let mut different_hasher = other_build_hasher.build_hasher(); /// different_hasher.write_u32(1234); /// assert_ne!(different_hasher.finish(), hasher_1.finish()); /// ``` /// [Hasher]: std::hash::Hasher /// [BuildHasher]: std::hash::BuildHasher /// [HashMap]: std::collections::HashMap #[inline] fn build_hasher(&self) -> AHasher { let (k0, k1) = scramble_keys(self.k0, self.k1); AHasher::new_with_keys(k0, k1) } } pub(crate) fn scramble_keys(k0: u64, k1: u64) -> (u64, u64) { //Scramble seeds (based on xoroshiro128+) //This is intentionally not similar the hash algorithm let result1 = k0.wrapping_add(k1); let k1 = k1 ^ k0; let k0 = k0.rotate_left(24) ^ k1 ^ (k1.wrapping_shl(16)); let result2 = k0.wrapping_add(k1.rotate_left(37)); (result2, result1) } #[cfg(test)] mod test { use crate::convert::Convert; use crate::*; use core::hash::BuildHasherDefault; use std::collections::HashMap; #[test] fn test_default_builder() { let mut map = HashMap::<u32, u64, BuildHasherDefault<AHasher>>::default(); map.insert(1, 3); } #[test] fn test_builder() { let mut map = HashMap::<u32, u64, ABuildHasher>::default(); map.insert(1, 3); } #[test] fn test_conversion() { let input: &[u8] = b"dddddddd"; let bytes: u64 = as_array!(input, 8).convert(); assert_eq!(bytes, 0x6464646464646464); } #[test] fn test_ahasher_construction() { let _ = AHasher::new_with_keys(1245, 5678); } }