fxhash has bad bit spread

[remram44]

I tried to use fxhash to distribute objects between buckets. To do this I use buckets[fxhash(value) % buckets.len()].

However I noticed that all objects ended up in the same bucket because the low-order bits (in fact the entire lower half of the digest) was constant.

This example shows the issue:

    for &value in &[b"00000001", b"00000002", b"00000003"] {
        let mut h = FxHasher::default();
        h.write(value);
        let r: u64 = h.finish();
        println!("{:08x}", r);
    }

output:

8eb24dfba44debf0
23b24dfba44debf0
b8b24dfba44debf0

Is this a known issue? Is there a recommended method for truncating the digest without losing too much entropy? This happens with a much higher number of test values too (tried 100,000 values formatted the same way).

fnv gives a better result in this case:

5bedc133e5925f92
5bedc033e5925ddf
5bedbf33e5925c2c

This might warrant a warning in the docs.

Playground link