Get n-th fibonacci number in Swift

fib.swift

import Foundation
import CoreFoundation

// MARK: Without recursion
func fib(_ n: Int) -> Int {
  guard n > 1 else { return n }
  var arr = Array.init(repeating: 1, count: n)
  for i in 2..<n {
      arr[i] = arr[i - 1] + arr[i - 2]
  }
  return arr.last!
}

// MARK: With recursion (a lot faster)
func fibR(_ n: Int) -> Int {
    guard n > 1 else { return n }
    return fibR(n - 1) + fibR(n - 2)
}

// MARK: Helper function for measure execution time
public func measure(label: String? = nil, tests: Int = 1, printResults output: Bool = true, setup: @escaping () -> Void = { return }, _ block: @escaping () -> Void) -> Double {
    
    guard tests > 0 else { fatalError("Number of tests must be greater than 0") }
    
    var avgExecutionTime : CFAbsoluteTime = 0
    for _ in 1...tests {
        setup()
        let start = CFAbsoluteTimeGetCurrent()
        block()
        let end = CFAbsoluteTimeGetCurrent()
        avgExecutionTime += end - start
    }
    
    avgExecutionTime /= CFAbsoluteTime(tests)
    
    if output {
        let avgTimeStr = "\(avgExecutionTime)".replacingOccurrences(of: "e|E", with: " × 10^", options: .regularExpression, range: nil)
        
        if let label = label {
            print(label, "▿")
            print("\tExecution time: \(avgTimeStr)s")
            print("\tNumber of tests: \(tests)\n")
        } else {
            print("Execution time: \(avgTimeStr)s")
            print("Number of tests: \(tests)\n")
        }
    }
    
    return avgExecutionTime
}

// MARK: Results

let timeNoR = measure(label: "Without recursion", printResults: true) {
  let n = fib(10)
  print("Without recursion: \(n)")
}

let timeR = measure(label: "Using recursion", printResults: true) {
  let n = fibR(10)
  print("Using recursion: \(n)")
}