string.unpack swift equivalent? - ruby

Question

I've been looking all over and can't seem to find an equivalent of String.unpack (ruby) for Swift. For example, I am trying to write these two statements in Swift:
offset = digest.unpack('#19C').first & 0x2f
value = digest.unpack("#{offset}#L").first
If anyone knows how I could accomplish this it would be very helpful, thank you!
EDIT:
Code so far:
import Foundation
class PasswordViewController: UIViewController {
#IBOutlet weak var simpleLabel: UILabel!
var email:String!
var LRA:String!
var sysid:String = "SECRET"
override func viewDidLoad() {
super.viewDidLoad()
var x:Int = 1446569017
reset_code(x)
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
func randomInt(min: Int, max:Int) -> Int {
return min + Int(arc4random_uniform(UInt32(max - min + 1)))
}
func reset_secret()->String {
return sysid.hmac(.SHA512, key: "THISISAKEY")
}
func reset_input(t:Int)->String{
var time:String = String(t)
var input:[String] = [sysid, email, time]
var stringrep:String = "|".join(input)
return stringrep
}
func reset_hmac(t:Int)->String{
var firstTime:String = reset_secret().hmac(.SHA256, key: reset_input(t))
return reset_secret().hmac(.SHA256, key: firstTime)
}
func reset_code(t:Int){
var time:Int = t / 43200
var digest:String = reset_hmac(t)
simpleLabel.text = digest
}
}
enum CryptoAlgorithm {
case SHA256, SHA512
var HMACAlgorithm: CCHmacAlgorithm {
var result: Int = 0
switch self {
case .SHA256: result = kCCHmacAlgSHA256
case .SHA512: result = kCCHmacAlgSHA512
}
return CCHmacAlgorithm(result)
}
var digestLength: Int {
var result: Int32 = 0
switch self {
case .SHA256: result = CC_SHA256_DIGEST_LENGTH
case .SHA512: result = CC_SHA512_DIGEST_LENGTH
}
return Int(result)
}
}
extension String {
func hmac(algorithm: CryptoAlgorithm, key: String) -> String {
let str = self.cStringUsingEncoding(NSUTF8StringEncoding)
let strLen = Int(self.lengthOfBytesUsingEncoding(NSUTF8StringEncoding))
let digestLen = algorithm.digestLength
let result = UnsafeMutablePointer<CUnsignedChar>.alloc(digestLen)
let keyStr = key.cStringUsingEncoding(NSUTF8StringEncoding)
let keyLen = Int(key.lengthOfBytesUsingEncoding(NSUTF8StringEncoding))
CCHmac(algorithm.HMACAlgorithm, keyStr!, keyLen, str!, strLen, result)
let digest = stringFromResult(result, length: digestLen)
result.dealloc(digestLen)
return digest
}
private func stringFromResult(result: UnsafeMutablePointer<CUnsignedChar>, length: Int) -> String {
var hash = NSMutableString()
for i in 0..<length {
hash.appendFormat("%02x", result[i])
}
return String(hash)
}
}