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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. extern crate const_random; extern crate arrayref; #[macro_use] mod convert; mod fallback_hash; #[cfg(all(any(target_arch = "x86", target_arch = "x86_64"), target_feature = "aes"))] mod aes_hash; #[cfg(test)] mod hash_quality_test; use const_random::const_random; use std::collections::HashMap; use std::hash::{BuildHasher, BuildHasherDefault}; #[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; /// A `HashMap` using a `BuildHasherDefault` BuildHasher to hash the items. pub type AHashMap<K, V> = HashMap<K, V, BuildHasherDefault<AHasher>>; ///Const random provides randomized keys with no runtime cost. const DEFAULT_KEYS: [u64;2] = [const_random!(u64), const_random!(u64)]; /// 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; /// use std::collections::HashMap; /// /// let mut map: HashMap<i32, i32, BuildHasherDefault<AHasher>> = HashMap::default(); /// map.insert(12, 34); /// ``` /// /// [BuildHasherDefault]: std::hash::BuildHasherDefault /// [Hasher]: std::hash::Hasher /// [HashMap]: std::collections::HashMap 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. /// /// # 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(DEFAULT_KEYS[0], DEFAULT_KEYS[1]) } } /// 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 pub struct ABuildHasher{} impl ABuildHasher { #[inline] pub fn new() -> ABuildHasher { ABuildHasher{} } } 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. /// /// # 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 mem_loc = self as *const _ as usize as u64; AHasher::new_with_keys(DEFAULT_KEYS[0], DEFAULT_KEYS[1] ^ mem_loc) } } #[cfg(test)] mod test { use crate::convert::Convert; use crate::*; #[test] fn test_builder() { let mut map = HashMap::<u32, u64, BuildHasherDefault<AHasher>>::default(); map.insert(1, 3); } #[test] fn test_conversion() { let input: &[u8] = "dddddddd".as_bytes(); let bytes: u64 = as_array!(input, 8).convert(); assert_eq!(bytes, 0x6464646464646464); } }