nathankrishnan

var badDomains: Set<String> = ["badguys.com", "drevil.me", "virus.io"]

let websiteToLoad = NSURL(string: "http://virus.io")
if let validDomain = websiteToLoad?.host {
    if badDomains.contains(validDomain) {
        print("This website is known to be malicious!")
    } else {
        print("This website doesn't exist in our dossier. Let's proceed.")
    }
}

nathankrishnan

print(MemoryLayout<Bool>.size)
// A Bool is represented with 1 byte

print(MemoryLayout<Int>.size)
// An Int is represented with 8 bytes

nathankrishnan

public class BloomFilter<T> {
    private var array: [Bool]
    private var hashFunctions: [(T) -> Int]
    
    public init(size: Int = 1024, hashFunctions: [(T) -> Int]) {
        self.array = [Bool](repeating: false, count: size)
        self.hashFunctions = hashFunctions
    }
    
    private func computeHashes(_ value: T) -> [Int]

nathankrishnan

private func computeHashes(_ value: T) -> [Int] {
  return hashFunctions.map() { hashFunction in abs(hashFunction(value) % array.count) }
}

nathankrishnan

private func computeHashes(_ value: T) -> [Int] {
  return hashFunctions.map({
    (hashFunction: (T) -> Int) -> Int in
      return abs(hashFunction(value)) % array.count
  })
}

nathankrishnan

private func computeHashes(_ value: T) -> [Int] {
    var results: [Int] = []
    for hashFunction in hashFunctions {
        let value = abs(hashFunction(value)) % array.count
        results.append(value)
    }
    return results
}

nathankrishnan

public func insert(_ element: T) {
  for hashValuePosition in computeHashes(element) {
    array[hashValuePosition] = true
  }
}

nathankrishnan

public func query(_ value: T) -> Bool {
    let hashValuePositions = computeHashes(value)
    let valuesAtIndices = hashValuePositions.map() { hashValuePosition in array[hashValuePosition] }
    let exists = valuesAtIndices.reduce(true, { $0 && $1 })
    return exists
}

nathankrishnan

public func isEmpty() -> Bool {
    return array.reduce(true) { prev, next in prev && !next }
}

nathankrishnan

let badDomains = BloomFilter<String>(size: 1024, hashFunctions: [djb2, sdbm])
badDomains.insert("badguys.com")
badDomains.insert("drevil.me")
badDomains.insert("virus.io")

let websiteToLoad = NSURL(string: "http://virus.io")
if let validDomain = websiteToLoad?.host {
    if badDomains.query(validDomain) {
        print("The website is most likely bad!")
    } else {