Port of the MurmurHash64A function from Redis.

murmurhash.rs

// Port of the MurmurHash64A function from Redis.
// Original here: https://github.com/antirez/redis/blob/93eed9ae0163e328c33b16ab9ea3c4fbe0f98674/src/hyperloglog.c#L390-L439

extern crate test;
use std::os;
use test::Bencher;

fn murmur_hash64a(key: &[u8], seed: u64) -> u64 {
    let m : u64 = 0xc6a4a7935bd1e995;
    let r : uint = 47;

    let len = key.len();
    let mut h : u64 = seed ^ (len as u64 * m);

    let endpos = len-(len&7);

    let mut i = 0u;
    while i != endpos {
        let mut k : u64;

        k  = key[i+0] as u64;
        k |= key[i+1] as u64 << 8;
        k |= key[i+2] as u64 << 16;
        k |= key[i+3] as u64 << 24;
        k |= key[i+4] as u64 << 32;
        k |= key[i+5] as u64 << 40;
        k |= key[i+6] as u64 << 48;
        k |= key[i+7] as u64 << 56;

        k *= m;
        k ^= k >> r;
        k *= m;
        h ^= k;
        h *= m;

        i += 8;
    };

    let over = len & 7;
    if over == 7 { h ^= key[i+6] as u64 << 48; }
    if over >= 6 { h ^= key[i+5] as u64 << 40; }
    if over >= 5 { h ^= key[i+4] as u64 << 32; }
    if over >= 4 { h ^= key[i+3] as u64 << 24; }
    if over >= 3 { h ^= key[i+2] as u64 << 16; }
    if over >= 2 { h ^= key[i+1] as u64 << 8; }
    if over >= 1 { h ^= key[i+0] as u64; }
    if over >  0 { h *= m; }

    h ^= h >> r;
    h *= m;
    h ^= h >> r;
    h
}

fn main() {
    let args = os::args();
    if args.len() != 3 {
        println!("Usage: {} key seed", args[0]);
        return
    }

    let key = args[1].clone();
    let seed : u64 = from_str(args[2].as_slice()).unwrap();

    println!("{:x}", murmur_hash64a(key.as_bytes(), seed));
}

#[bench]
fn benchmark_murmur(b: &mut Bencher) {
    let key = "lorem ipsum dolor sit amet".as_bytes();
    let seed = 0xadc83b19;
    b.iter(|| {
        murmur_hash64a(key, seed);
    })
}