Rust bindings to Google CityHash's C++ API.
CityHash-sys do not load the standard library (a.k.a no_std).
Table of contents 1. Introduction 2. Usage 1. Using Hasher 2. Using Portable CityHash functions 3. Using CityHash functions with CRC-32 intrinsic 4. Using Rust convenient traits 3. Performance 4. For more information
CityHash provides hash functions for strings. Functions mix the input bits thoroughly but are not suitable for cryptography. CityHash-sys is tested on little-endian but should work on big-endian architecture.
```rust use cityhash_sys::CityHashBuildHasher; use std::collections::HashMap; const KEY: &str = "hash"; const VALUE: &str = "me!";
// Create a HashMap that use CityHash64 to hash keys let mut map = HashMap::with_hasher(CityHashBuildHasher::default()); map.insert(KEY, VALUE);
assert_eq!(map.get(&KEY), Some(&VALUE));
``
**_Note_** *CityHashBuildHasheris an alias to the the 64-bits CityHashCityHash64Hasher.CityHash32HasherandCityHash128Hasherare also available but result are stillu64`. See documentation for more details.*
Rust bindings provides a safe interface to all Google's CityHash hash functions that do not make use of x86_64 CRC intrinsic:
32-bit hash
rust ignore
// uint32 CityHash32(const char *, size_t);
fn city_hash_32(buf: &[u8]) -> u32;
64-bit hash
```rust ignore // uint64 CityHash64(const char *, sizet); fn cityhash_64(buf: &[u8]) -> u64;
// uint64 CityHash64WithSeed(const char *, sizet, uint64); fn cityhash64with_seed(buf: &[u8], seed: u64) -> u64;
// uint64 CityHash64WithSeeds(const char *, sizet, uint64, uint64); fn cityhash64withseeds(buf: &[u8], seed0: u64, seed_1: u64) -> u64; ```
128-bit hash
```rust ignore // uint128 CityHash128(const char *, sizet); fn cityhash_128(buf: &[u8]) -> u128;
// uint128 CityHash128WithSeed(const char *, sizet, uint128); fn cityhash128with_seed(buf: &[u8], seed: u128) -> u128;
// uint64 Hash128to64(const uint128&); fn cityhash128to64(hash: u128) -> u64; ```
Note: Depending on your compiler and hardware, it's likely faster than CityHash64() on sufficiently long strings. It's slower than necessary on shorter strings.
Some functions are available only if the target is x86_64 and support at least sse4.2 target feature because of the usage of CRC-32 intrinsic _mm_crc32_u64 . If we want to enable those functions use -C target-feature=+sse4.2 or above (avx or avx2).
Note that depending of the length of the buffer you want to hash, it can be faster to use the non-intrinsic version.
If the buffer to hash is less than 900 bytes, CityHashCrc128WithSeed and CityHashCrc128 will respectivelly internally call CityHash128WithSeed and CityHash128, in this case, it is better to call directly CityHash128WithSeed or CityHash128.
128-bit hash with CRC-32 intrinsic
```rust ignore // uint128 CityHashCrc128(const char *, sizet); fn cityhashcrc128(buf: &[u8]) -> u128;
// uint128 CityHashCrc128WithSeed(const char *, sizet, uint128); fn cityhashcrc128withseed(buf: &[u8], seed: u128) -> u128; ```
256-bit hash with CRC-32 intrinsic
rust ignore
// void CityHashCrc256(const char *, size_t, uint64 *);
fn city_hash_crc_256(buf: &[u8]) -> [u64; 4]; //
CityHash-sys provides convenient traits to hash.
CityHash trait provides hash functions that do not used the CRC-32 intrinsics.
```rust use cityhash_sys::CityHash;
// Hash the slice with CityHash64 let hashslice: u64 = [5u8, 4, 3, 2, 1].cityhash64(); asserteq!(hash_slice, 0x34EC5F7922A51496);
// Hash the str with CityHash64 let hashstr: u64 = "hash me!".cityhash64(); asserteq!(hash_str, 0xF04A0CC67B63A0B4); ```
CityHashCrc trait provides hash implementation for [u8] and str types with x86_64 CRC-32 intrinsic. (Only available with target-feature=+sse4.2)
```rust use cityhash_sys::CityHashCrc;
// Hash the slice with CityHashCrc128 let hashcrcslice: u128 = [5u8, 4, 3, 2, 1].cityhashcrc_128();
// Hash the str with CityHashCrc128 let hashcrcslice: u128 = "hash me!".cityhashcrc_128(); ```
On 64-bits hardware, CityHash is suitable for short string hashing, e.g., most hash table keys, especially city_hash_64 that is faster than city_hash_128.
On 32-bits hardware, CityHash is the nearest competitor of Murmur3 on x86.
See the Google Cityhash README
