hash_hasher 2.0.3

A hasher which is designed to work with already-hashed or hash-like data.


A std::hash::Hasher which is designed to work with already-hashed or hash-like data.

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The provided hasher does minimal work under the assumption that the input data is already suitable for use as a key in a HashSet or HashMap.

As well as the performance benefit, it also causes HashSets or HashMaps to become somewhat deterministic. Given two equal HashSets or HashMaps containing more than a single element, iterating them will yield the elements in differing orders. By using a hash_hasher::HashedSet or hash_hasher::HashedMap, then if the same data is inserted and/or removed in the same order, iterating the collection will yield a consistent order.


Since new() and with_capacity() aren't available for HashSets or HashMaps using custom hashers, the available constructors are default(), with_hasher() and with_capacity_and_hasher().

extern crate hash_hasher;

use hash_hasher::{HashBuildHasher, HashedMap, HashedSet};

let mut map = HashedMap::default();
assert!(map.insert(0, "zero").is_none());

let mut set = HashedSet::with_capacity_and_hasher(100, HashBuildHasher::default());


A benchmark suite is included and sample figures can be found at the end of the nightly jobs of the AppVeyor results and the Travis results.

For example:

insert_sha1s_into_set_using_default_hasher      ... bench:       1,171 ns/iter (+/- 30)
insert_sha1s_into_set_using_hash_hasher         ... bench:         533 ns/iter (+/- 9)

insert_sha256s_into_set_using_default_hasher    ... bench:       1,340 ns/iter (+/- 57)
insert_sha256s_into_set_using_hash_hasher       ... bench:         546 ns/iter (+/- 11)

insert_sha512s_into_set_using_default_hasher    ... bench:       1,804 ns/iter (+/- 2,597)
insert_sha512s_into_set_using_hash_hasher       ... bench:         704 ns/iter (+/- 22)

insert_sip_hashes_into_set_using_default_hasher ... bench:         781 ns/iter (+/- 33)
insert_sip_hashes_into_set_using_hash_hasher    ... bench:         256 ns/iter (+/- 50)


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Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.