Reproducible Hashes is 0.8? about ahash

[rrichardson]

@domenukk - digging into the code a bit farther, it seems that using RandomState::with_seeds should achieve the old new_with_keys functionality.

e.g.

let st = RandomState::with_seeds(42, 1, 0 5); 
let hasher = st.build_hasher(); 

build_hasher just calls (private) AHasher::from_random_state (https://docs.rs/ahash/latest/src/ahash/aes_hash.rs.html#73)

However, I still don't get consistency across multiple platforms (and I suspect 0.7 is the same)

[rrichardson]

I am in a similar boat. I've tried setting
default-features = false
then doing :

static HASH_KEY: usize = 12345;

lazy_static! {
    static ref HASH_STATE: RandomState = { 
        set_random_source(NotRandomState).expect("Setting hash state to not-random");
        RandomState::with_seed(HASH_KEY)
    };
}
struct NotRandomState;

impl RandomSource for NotRandomState {
    fn gen_hasher_seed(&self) -> usize {
        HASH_KEY
    }
}

fn hash_stuff(a: A, b: B) -> u64 {
    let mut hasher = HASH_STATE.build_hasher();
    a.hash(&mut hasher);
    b.hash(&mut hasher);
    hasher.finish().into()
}

This seems to produce self-consistent hashes between builds on the same platform.

However, on different platforms (e.g. aarch64) it produces different values.

Is there an easier or more reliable method of ensuring consistencency?

[tkaitchuck]

with_seeds is the method you are looking for.
However please note that aHash does not guarantee identical output across architectures, flags, or versions. For example when 0.8.1 is released, it will have performance improvements but the same data will hash to different values than it did in 0.8.0.

[tkaitchuck]

This is now better documented in 0.8.1:
https://docs.rs/ahash/0.8.1/ahash/random_state/struct.RandomState.html