Swift md5加密

public func md5(strs:String) ->String!{
  let str = strs.cString(using: String.Encoding.utf8)
  let strLen = CUnsignedInt(strs.lengthOfBytes(using: String.Encoding.utf8))
  let digestLen = Int(CC_MD5_DIGEST_LENGTH)
  let result = UnsafeMutablePointer<CUnsignedChar>.allocate(capacity: digestLen)
  CC_MD5(str!, strLen, result)
  let hash = NSMutableString()
  for i in 0 ..< digestLen {
      hash.appendFormat("%02x", result[i])
  }
  result.deinitialize()
  return String(format: hash as String)
}