I want multiple non-random numbers in swift - ios

Question

I am using swift and want to have a number of duplicatable patterns throughout my game.
Ideally I would have some sort of shared class that worked sort of like this (this is sort of pseudo-Swift code):
class RandomNumberUtility {
static var sharedInstance = RandomNumberUtility()
var random1 : Random()
var random2 : Random()
func seedRandom1(seed : Int){
random1 = Random(seed)
}
func seedRandom2(seed : Int){
random2 = Random(seed)
}
func getRandom1() -> Int {
return random1.next(1,10)
}
func getRandom2() -> Int {
return random2.next(1,100)
}
}
Then, to begin the series, anywhere in my program I could go like this:
RandomNumberUtility.sharedInstance.seedNumber1(7)
RandomNumberUtility.sharedInstance.seedNumber2(12)
And then I would know that (for example) the first 4 times I called
RandomNumberUtility.sharedInstance.getRandom1()
I would always get the same values (for example: 6, 1, 2, 6)
This would continue until at some point I seeded the number again, and then I would either get the exact same series back (if I used the same seed), or a different series (if I used a different seed).
And I want to have multiple series of numbers (random1 & random2) at the same time.
I am not sure how to begin to turn this into an actual Swift class.

Answer 1

Here is a possible implementation. It uses the jrand48 pseudo random number generator,
which produces 32-bit numbers.
This PRNG is not as good as arc4random(), but has the advantage
that all its state is stored in a user-supplied array, so that multiple
instances can run independently.
struct RandomNumberGenerator {
// 48 bit internal state for jrand48()
private var state : [UInt16] = [0, 0, 0]
// Return pseudo-random number in the range 0 ... upper_bound-1:
mutating func next(upper_bound: UInt32) -> UInt32 {
// Implementation avoiding the "module bias" problem,
// taken from: http://stackoverflow.com/a/10989061/1187415,
// Swift translation here: http://stackoverflow.com/a/26550169/1187415
let range = UInt32.max - UInt32.max % upper_bound
var rnd : UInt32
do {
rnd = UInt32(truncatingBitPattern: jrand48(&state))
} while rnd >= range
return rnd % upper_bound
}
mutating func seed(newSeed : Int) {
state[0] = UInt16(truncatingBitPattern: newSeed)
state[1] = UInt16(truncatingBitPattern: (newSeed >> 16))
state[2] = UInt16(truncatingBitPattern: (newSeed >> 32))
}
}
Example:
var rnd1 = RandomNumberGenerator()
rnd1.seed(7)
var rnd2 = RandomNumberGenerator()
rnd2.seed(12)
println(rnd1.next(10)) // 2
println(rnd1.next(10)) // 8
println(rnd1.next(10)) // 1
println(rnd2.next(10)) // 6
println(rnd2.next(10)) // 0
println(rnd2.next(10)) // 5
If rnd1 is seeded with the same value as above then it
produces the same numbers again:
rnd1.seed(7)
println(rnd1.next(10)) // 2
println(rnd1.next(10)) // 8
println(rnd1.next(10)) // 1

Answer 2

What you need is a singleton that generates pseudo-random numbers and make sure all your code that need a random number call via this class. The trick is to reset the seed for each run of your code. Here is a simple RandomGenerator class that will do the trick for you (it's optimized for speed which is a good thing when writing games):
import Foundation
// This random number generator comes from: Klimov, A. and Shamir, A.,
// "A New Class of Invertible Mappings", Cryptographic Hardware and Embedded
// Systems 2002, http://dl.acm.org/citation.cfm?id=752741
//
// Very fast, very simple, and passes Diehard and other good statistical
// tests as strongly as cryptographically-secure random number generators (but
// is not itself cryptographically-secure).
class RandomNumberGenerator {
static let sharedInstance = RandomNumberGenerator()
private init(seed: UInt64 = 12347) {
self.seed = seed
}
func nextInt() -> Int {
return next(32)
}
private func isPowerOfTwo(x: Int) -> Bool { return x != 0 && ((x & (x - 1)) == 0) }
func nextInt(max: Int) -> Int {
assert(!(max < 0))
// Fast path if max is a power of 2.
if isPowerOfTwo(max) {
return Int((Int64(max) * Int64(next(31))) >> 31)
}
while (true) {
var rnd = next(31)
var val = rnd % max
if rnd - val + (max - 1) >= 0 {
return val
}
}
}
func nextBool() -> Bool {
return next(1) != 0
}
func nextDouble() -> Double {
return Double((Int64(next(26)) << 27) + Int64(next(27))) /
Double(Int64(1) << 53)
}
func nextInt64() -> Int64 {
let lo = UInt(next(32))
let hi = UInt(next(32))
return Int64(UInt64(lo) | UInt64(hi << 32))
}
func nextBytes(inout buffer: [UInt8]) {
for n in 0..<buffer.count {
buffer[n] = UInt8(next(8))
}
}
var seed: UInt64 {
get {
return _seed
}
set(seed) {
_initialSeed = seed
_seed = seed
}
}
var initialSeed: UInt64 {
return _initialSeed!
}
private func randomNumber() -> UInt32 {
_seed = _seed &+ ((_seed &* _seed) | 5)
return UInt32(_seed >> 32)
}
private func next(bits: Int) -> Int {
assert(bits > 0)
assert(!(bits > 32))
return Int(randomNumber() >> UInt32(32 - bits))
}
private var _initialSeed: UInt64?
private var _seed: UInt64 = 0
}