From 94c41facd0b9fee711245f1f09973669499114a7 Mon Sep 17 00:00:00 2001
From: Justin Mazzocchi <2831158+jzzocc@users.noreply.github.com>
Date: Sun, 6 Sep 2020 02:18:32 -0700
Subject: [PATCH] Add more hashers

---
 .../DeterministicHasher.swift                 | 22 +++++++++++++++----
 .../CodableBloomFilterTests.swift             | 12 +++++++++-
 2 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/CodableBloomFilter/Sources/CodableBloomFilter/DeterministicHasher.swift b/CodableBloomFilter/Sources/CodableBloomFilter/DeterministicHasher.swift
index 650bc73..acb7748 100644
--- a/CodableBloomFilter/Sources/CodableBloomFilter/DeterministicHasher.swift
+++ b/CodableBloomFilter/Sources/CodableBloomFilter/DeterministicHasher.swift
@@ -4,33 +4,47 @@ import Foundation
 
 public enum DeterministicHasher: String, Codable {
     case djb2
+    case djb2a
     case sdbm
+    case fnv1
+    case fnv1a
 }
 
 extension DeterministicHasher {
     func apply(_ hashable: DeterministicallyHashable) -> Int {
         Array(hashable.hashableData)
             .map(Int.init)
-            .reduce(initial, then)
+            .reduce(offsetBasis, hash)
     }
 }
 
 // http://www.cse.yorku.ca/~oz/hash.html
+// http://www.isthe.com/chongo/tech/comp/fnv/
 
 private extension DeterministicHasher {
-    var initial: Int {
+    static let fnvPrime = 16777619
+    static let u32mod = 2 << 31
+
+    var offsetBasis: Int {
         switch self {
-        case .djb2: return 5381
+        case .djb2, .djb2a: return 5381
         case .sdbm: return 0
+        case .fnv1, .fnv1a: return 2166136261
         }
     }
 
-    func then(result: Int, next: Int) -> Int {
+    func hash(result: Int, next: Int) -> Int {
         switch self {
         case .djb2:
             return (result << 5) &+ result &+ next
+        case .djb2a:
+            return ((result << 5) &+ result ^ next) % Self.u32mod
         case .sdbm:
             return next &+ (result << 6) &+ (result << 16) - result
+        case .fnv1:
+            return (result * Self.fnvPrime % Self.u32mod) ^ next
+        case .fnv1a:
+            return (result ^ next) * Self.fnvPrime % Self.u32mod
         }
     }
 }
diff --git a/CodableBloomFilter/Tests/CodableBloomFilterTests/CodableBloomFilterTests.swift b/CodableBloomFilter/Tests/CodableBloomFilterTests/CodableBloomFilterTests.swift
index 623fe2d..0d55260 100644
--- a/CodableBloomFilter/Tests/CodableBloomFilterTests/CodableBloomFilterTests.swift
+++ b/CodableBloomFilter/Tests/CodableBloomFilterTests/CodableBloomFilterTests.swift
@@ -1,9 +1,19 @@
+// Copyright © 2020 Metabolist. All rights reserved.
+
 @testable import CodableBloomFilter
 import XCTest
 
 final class CodableBloomFilterTests: XCTestCase {
+    func testHashers() {
+        XCTAssertEqual(DeterministicHasher.djb2.apply("hash"), 6385287881)
+        XCTAssertEqual(DeterministicHasher.djb2a.apply("hash"), 2087809207)
+        XCTAssertEqual(DeterministicHasher.sdbm.apply("hash"), 29358318056884782)
+        XCTAssertEqual(DeterministicHasher.fnv1.apply("hash"), 0xd7918815)
+        XCTAssertEqual(DeterministicHasher.fnv1a.apply("hash"), 0xcec577d1)
+    }
+
     func testContains() {
-        var sut = BloomFilter<String>(hashers: [.djb2, .sdbm], byteCount: 128)
+        var sut = BloomFilter<String>(hashers: [.djb2, .sdbm, .fnv1, .fnv1a], byteCount: 128)
 
         sut.insert("lol")
         sut.insert("ok")