Skip to content

Instantly share code, notes, and snippets.

Embed
What would you like to do?
Swift Hash Functions
import Foundation
struct Country {
let name: String
let capital: String
var visited: Bool
}
extension Country: Equatable {
static func == (lhs: Country, rhs: Country) -> Bool {
return lhs.name == rhs.name &&
lhs.capital == rhs.capital &&
lhs.visited == rhs.visited
}
}
extension Country: Comparable {
static func < (lhs: Country, rhs: Country) -> Bool {
return lhs.name < rhs.name ||
(lhs.name == rhs.name && lhs.capital < rhs.capital) ||
(lhs.name == rhs.name && lhs.capital == rhs.capital && rhs.visited)
}
}
// http://www.cse.yorku.ca/~oz/hash.html
extension String {
// hash(0) = 5381
// hash(i) = hash(i - 1) * 33 ^ str[i];
var djb2hash: Int {
let unicodeScalars = self.unicodeScalars.map { $0.value }
return unicodeScalars.reduce(5381) {
($0 << 5) &+ $0 &+ Int($1)
}
}
// hash(0) = 0
// hash(i) = hash(i - 1) * 65599 + str[i];
var sdbmhash: Int {
let unicodeScalars = self.unicodeScalars.map { $0.value }
return unicodeScalars.reduce(0) {
Int($1) &+ ($0 << 6) &+ ($0 << 16) - $0
}
}
}
// https://github.com/krzysztofzablocki/Sourcery
// MIT License
//
// Copyright (c) 2016 Krzysztof Zabłocki
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
fileprivate func combineHashes(_ hashes: [Int]) -> Int {
return hashes.reduce(0, combineHashValues)
}
fileprivate func combineHashValues(_ initial: Int, _ other: Int) -> Int {
#if arch(x86_64) || arch(arm64)
let magic: UInt = 0x9e3779b97f4a7c15
#elseif arch(i386) || arch(arm)
let magic: UInt = 0x9e3779b9
#endif
var lhs = UInt(bitPattern: initial)
let rhs = UInt(bitPattern: other)
lhs ^= rhs &+ magic &+ (lhs << 6) &+ (lhs >> 2)
return Int(bitPattern: lhs)
}
// Three different approachs to combining the hash values
// of the properties of a structure.
extension Country: Hashable {
// XOR the three values. Simple and works well in this case
// where we do not expect our name and capital to have
// matching values.
var simpleHashValue: Int {
return name.hashValue ^ capital.hashValue ^ visited.hashValue
}
// Avoid common collisions when name and capital can have
// matching values by applying a different hash method to
// one of the values
var djb2HashValue: Int {
return name.djb2hash ^ capital.hashValue ^ visited.hashValue
}
// Use the boost hash combine function to combine an array
// of hashValues.
var boostHashValue: Int {
return combineHashes([name.hashValue,capital.hashValue,visited.hashValue])
}
// Return the hash value using one of the above approaches
var hashValue: Int {
return boostHashValue
}
}
@PWrzesinski

This comment has been minimized.

Copy link

PWrzesinski commented Sep 24, 2019

String.sdbmhash crashed on the first run

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
You can’t perform that action at this time.