Mesure performance of ranges compared to suffixing and prefixing

subscript-vs-fixes.swift

//               Results
//       Range      vs   Prefix&Suffix
// 5.88606303930283 vs 9.89196902513504 - Manipulating Array 
// 5.65134799480438 vs 5.69769901037216 - Manipulating String

func measure(closure: (()->Void)) {
    let start = Date()
    closure()
    let interval = Date().timeIntervalSince(start)
    print(interval)
}

let values: [String] = Array(repeating: "a0", count: 2400)

// 5.88606303930283 sec
measure {

    let numberOfPeers = values.count/6
    var peers: [(ip: String, port: Int)] = []
    
    for i in 0..<numberOfPeers {

        let offset = i*6

        let ip = values[offset..<offset+4].map{ String(Int($0, radix: 16)!) }.joined(separator: ".")
        let port = values[offset+4..<offset+6].reduce(0) { $0 * Int(UInt8.max) + Int($1, radix: 16)! }
        peers.append((ip: ip, port: port))
    }
}

// 9.89196902513504 sec
measure {
    
    var addresses = values.suffix(values.count)
    var peers: [(ip: String, port: Int)] = []
    var offset = 0
    
    while addresses.count > 0 {
        let ip = addresses.prefix(upTo: offset+4).map{ String(Int($0, radix: 16)!) }.joined(separator: ".")
        addresses = addresses.suffix(from: offset+4)
        let port = addresses.prefix(upTo: offset+6).reduce(0) { $0 * Int(UInt8.max) + Int($1, radix: 16)! }
        addresses = addresses.suffix(from: offset+6)
        offset += 6
        peers.append((ip: ip, port: port))
    }
}

extension String {
    
    subscript (r: Range<Int>) -> String {
        let start = index(startIndex, offsetBy: r.lowerBound)
        let end = index(startIndex, offsetBy: r.upperBound)
        return String(self[Range(start ..< end)])
    }
}

let string = values.joined()
string.count

// 5.65134799480438 sec
measure {
    
    let numberOfPeers = string.count/12
    var peers: [(ip: String, port: String)] = []
    
    for i in 0..<numberOfPeers {
        
        let offset: Int = i*6
        
        let ip = string[offset..<offset+8]
        // values[offset..<offset+4].map{ String(Int($0, radix: 16)!) }.joined(separator: ".")
        let port = string[offset+8..<offset+12]
        // values[offset+4..<offset+6].reduce(0) { $0 * Int(UInt8.max) + Int($1, radix: 16)! }
        peers.append((ip: ip, port: port))
    }
    
}

// 5.69769901037216 sec
measure {
    
    var peers: [(ip: String, port: String)] = []
    var text = string
    
    while text.count > 0 {
        
        let ipEnd = text.index(text.startIndex, offsetBy: 8)
        let ip = String(text.prefix(upTo: ipEnd))
        text = String(text.suffix(from: ipEnd))
        let portEnd = text.index(text.startIndex, offsetBy: 4)
        let port = String(text.prefix(upTo: portEnd))
        text = String(text.suffix(from: portEnd))
        
        peers.append((ip: ip, port: port))
    }
    
}