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FowlerNollVo

A FNV-1 implementation in Swift. This package has no dependencies. The minimum swift-tools version to build this package is 5.0. See documentation here.

FNV-1 is a simple non-cryptographic hash function. You can learn more about it here.

Platforms

This project is tested in continuous integration on the following platforms:

  • Ubuntu 20.04 LTS
  • Windows Server 2019
  • macOS 11.5
  • iOS 15.2
  • tvOS 15.2
  • watchOS 8.3

Installation

FowlerNollVo is a Swift Package Manager project. To depend on it, include it in your Package.swift dependencies:

.package(
    name: "FowlerNollVo", 
    url: "https://github.com/crichez/swift-fowler-noll-vo", 
    .upToNextMinor(from: "0.2.0")),

All versions below 1.0.0 are considered pre-release. This means code-breaking changes may be added with a minor version bump. To avoid this, use the .upToNextMinor(from:) version method in your package manifest, like in the example above. Once the project graduates to 1.0.0, regular semantic versioning rules will apply.

FNVHashable

This protocol intends to closely mirror the Swift standard library Hashable protocol. You can make your custom types conform to FNVHashable to hash them with a FNVHasher.

The code looks almost exactly the same:

import FowlerNollVo

struct MyCustomType: FNVHashable {
    let id: Int
    var name: String
    var quality: Double
    
    func hash<Hasher>(into hasher: inout Hasher) where Hasher : FNVHasher {
        hasher.combine(id)
        hasher.combine(name)
        hasher.combine(quality)
    }
}

Hashers

The following hasher types are built-in:

  • FNV32 & FNV32a
  • FNV64 & FNV64a
  • FNV128 & FNV128a
  • FNV256 & FNV256a
  • FNV512 & FNV512a
  • FNV1024 & FNV1024a

Note: FNV128 and hashers with larger digests all use DoubleWidth from the swift numerics project. That code was included in this project under its original Apache 2.0 license, and is still considered experimental.

Although performance from 32 to 64-bit digests is similar, performance quickly degrades with larger digests. Getting a 1024-bit digest from 64 bits of input data takes around 0.33 seconds on a M1 MacBook Pro.

Usage

import FowlerNollVo

var hasher = FNV64a()

hasher.combine(12)
hasher.combine("this is a string!")
hasher.combine(MyCustomType())

let digest: UInt64 = hasher.digest