9 Replies
      Latest reply on Feb 15, 2019 2:43 AM by eskimo
      DANO Level 1 Level 1 (0 points)

        Here's my delimna: I am writing an application that needs to exactly reproduce the PRNG output from a game that was written in Java that uses the Java random() with a given seed to create all it's initial game 'world' data.

        The problem I am facing is that Java's random() and ios Swift native PRNG do not generate the same values when given the exact same seeds.

        Here are my test cases: In all cases the same 'seed' is used, and the formula is for a random Integer between 0 and 9.


        In Java:

        import java.util.Random;
        long seed = 987234904; 
        Random rnd = new Random(seed); 
        int result = rnd.nextInt(10);

        The Java random() 'result' = 0


        Swift - using srand48() / drand48():

        import UIKit 
        var seed: Int = 987234904 
        var result = Int(drand48()*10)

        The ios Swift drand48() 'result' = 7


        In Swift - using rand_r():

        import UIKit 
        var seed: UInt32 = 987234904 
        var result = Int(Float(rand_r(&seed))/Float(INT32_MAX)*10)

        The ios Swift rand_r() result = 4


        In Swift - using the new GKLinearCongruentialRandomSource - which uses a simular Linear Congruential method that Java.util.random() was based on - suposedly:

        import UIKit 
        import GameplayKit 
        if #available (iOS 9,*) { 
           let seed: UInt64 = 987234904 
           let random = GKLinearCongruentialRandomSource(seed: seed) 
           let result = random.nextIntWithUpperBound(10) // should be a random Int from 0 to 9 (total 10 possibilities }

        result = 6


        With that in mind - is there a ios Swift|Objective-C|C++ code snippit|library available that is the exact same in functionality and output as the Java's version of random()?