Module murmur2

Murmur2, a suite of non-cryptographic hash functions that was used for hash-based lookups.

by Austin Appleby (aappleby (AT) gmail)

https://sites.google.com/site/murmurhash/

Extremely simple - compiles down to ~52 instructions on x86.

Excellent distribution - Passes chi-squared tests for practically all keysets & bucket sizes.

Excellent avalanche behavior - Maximum bias is under 0.5%.

Excellent collision resistance - Passes Bob Jenkin’s frog.c torture-test. No collisions possible for 4-byte keys, no small (1- to 7-bit) differentials.

Excellent performance - measured on an Intel Core 2 Duo @ 2.4 ghz

• OneAtATime - 354.163715 mb/sec
• FNV - 443.668038 mb/sec
• SuperFastHash - 985.335173 mb/sec
• lookup3 - 988.080652 mb/sec
• MurmurHash 1.0 - 1363.293480 mb/sec
• MurmurHash 2.0 - 2056.885653 mb/sec

Variants

The current version is MurmurHash3, which yields a 32-bit or 128-bit hash value.

The older MurmurHash2 yields a 32-bit or 64-bit value. Slower versions of MurmurHash2 are available for big-endian and aligned-only machines. The MurmurHash2A variant adds the Merkle–Damgård construction so that it can be called incrementally. There are two variants which generate 64-bit values; MurmurHash64A, which is optimized for 64-bit processors, and MurmurHash64B, for 32-bit ones.

Attacks

MurmurHash was a recommended hash function for hash table implementations. Jean-Philippe Aumasson and Daniel J. Bernstein were able to show that even randomized implementations of MurmurHash are vulnerable to so-called [HashDoS attacks] (https://emboss.github.io/blog/2012/12/14/breaking-murmur-hash-flooding-dos-reloaded/). With the use of differential cryptanalysis they were able to generate inputs that would lead to a hash collision. This can be abused to cause very slow operations of a hash table implementation. The authors of the attack recommend to use SipHash instead.

Example

use std::hash::{Hash, Hasher};

use fasthash::{murmur2, Murmur2Hasher};

fn hash<T: Hash>(t: &T) -> u64 {
    let mut s: Murmur2Hasher = Default::default();
    t.hash(&mut s);
    s.finish()
}

let h = murmur2::hash64(b"hello world\xff");

assert_eq!(h, hash(&"hello world"));

Structs

Hash32

MurmurHash2 32-bit hash functions

Hash32A

MurmurHash2A 32-bit hash functions

Hash32Aligned

MurmurHash2 32-bit aligned hash functions for the little-endian aligned-read-only implementation

Hash32Neutral

MurmurHash2 32-bit neutral hash functions for the (slower) endian-neutral implementation

Hash64_x64

MurmurHash2 64-bit hash functions for 64-bit processors

Hash64_x86

MurmurHash2 64-bit hash functions for 32-bit processors

Hasher32

An implementation of std::hash::Hasher.

Hasher32A

An implementation of std::hash::Hasher.

Hasher32Aligned

An implementation of std::hash::Hasher.

Hasher32Neutral

An implementation of std::hash::Hasher.

Hasher64_x64

An implementation of std::hash::Hasher.

Hasher64_x86

An implementation of std::hash::Hasher.

Functions

hash32

MurmurHash2 32-bit hash functions for a byte array.

hash64

MurmurHash2 64-bit hash functions for a byte array.

hash32_with_seed

MurmurHash2 32-bit hash function for a byte array. For convenience, a 32-bit seed is also hashed into the result.

hash64_with_seed

MurmurHash2 64-bit hash function for a byte array. For convenience, a 64-bit seed is also hashed into the result.