Crate hash32

32-bit hashing algorithms

Why?

Because 32-bit architectures are a thing (e.g. ARM Cortex-M) and you don’t want your hashing function to pull in a bunch of slow 64-bit compiler intrinsics (software implementations of 64-bit operations).

Relationship to core::hash

This crate extends core::hash with a 32-bit version of Hasher, which extends core::hash::Hasher. It requires that the hasher only performs 32-bit operations when computing the hash, and adds finish32 to get the hasher’s result as a u32. The standard finish method should just zero-extend this result.

Since it extends core::hash::Hasher, Hasher can be used with any type which implements the standard Hash trait.

This crate also adds a version of BuildHasherDefault with a const constructor, to work around the core version’s lack of one.

Hashers

This crate provides implementations of the following 32-bit hashing algorithms:

• Fowler-Noll-Vo
• MurmurHash3

Generic code

In generic code, the trait bound H: core::hash::Hasher accepts both 64-bit hashers like std::collections::hash_map::DefaultHasher; and 32-bit hashers like the ones defined in this crate (hash32::FnvHasher and hash32::Murmur3Hasher)

The trait bound H: hash32::Hasher is more restrictive as it only accepts 32-bit hashers.

The BuildHasherDefault<H> type implements the core::hash::BuildHasher trait so it can construct both 32-bit and 64-bit hashers. To constrain the type to only produce 32-bit hasher you can add the trait bound H::Hasher: hash32::Hasher

MSRV

This crate is guaranteed to compile on latest stable Rust. It might compile on older versions but that may change in any new patch release.

Structs

• BuildHasherDefault
  A copy of core::hash::BuildHasherDefault, but with a const constructor.
• FnvHasher
  32-bit Fowler-Noll-Vo hasher
• Murmur3Hasher
  32-bit MurmurHash3 hasher

Traits

• Hasher
  An extension of core::hash::Hasher for hashers which use 32 bits.