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50 lines
1.2 KiB
Swift
50 lines
1.2 KiB
Swift
// Copyright © 2020 Metabolist. All rights reserved.
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import Foundation
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public enum Hash: String, Codable {
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case djb232
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case djb2a32
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case sdbm32
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case fnv132
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case fnv1a32
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}
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extension Hash {
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func apply(_ hashable: DeterministicallyHashable) -> Int {
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Int(Array(hashable.dataForHashingDeterministically)
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.map(UInt32.init)
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.reduce(offsetBasis, hash))
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}
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}
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// http://www.cse.yorku.ca/~oz/hash.html
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// http://www.isthe.com/chongo/tech/comp/fnv/
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private extension Hash {
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static let fnvPrime: UInt32 = 16777619
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var offsetBasis: UInt32 {
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switch self {
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case .djb232, .djb2a32: return 5381
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case .sdbm32: return 0
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case .fnv132, .fnv1a32: return 2166136261
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}
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}
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func hash(result: UInt32, next: UInt32) -> UInt32 {
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switch self {
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case .djb232:
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return (result << 5) &+ result &+ next
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case .djb2a32:
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return (result << 5) &+ result ^ next
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case .sdbm32:
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return next &+ (result << 6) &+ (result << 16) &- result
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case .fnv132:
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return (result &* Self.fnvPrime) ^ next
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case .fnv1a32:
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return (result ^ next) &* Self.fnvPrime
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}
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}
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}
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