Math.random on Android

pozirk · April 17, 2019, 9:01pm

Hi!

I have cards game and getting comment from players that cards are not dealt randomly anymore.
I use simple Math.random, I also do untyped __cpp__('srand(time(NULL))'); on the app launch.
Everything seems pretty random on other platforms and my test devices.
Does anyone has any similar problems?

Thank you!

singmajesty · April 19, 2019, 5:44am

Does time(NULL) print a value that looks unique each time you run the application on Android?

EDIT: Or maybe this: https://stackoverflow.com/questions/18116733/any-function-in-c-or-java-android-could-mess-up-srand

Vega · April 19, 2019, 7:49am

Using Math.random for my card games too(Fisher–Yates shuffle).
But i dont seed with srand.

So far no complains and it looks random every time.

pozirk · April 19, 2019, 3:16pm

@singmajesty, it’s always different for me, increasing as it has to.
@Vega, Math.random is random for me and 99% of the players, only few have this problem.
My only guess, their devices are hacked.
Unfortunately, those few players complain, but can’t debug for me.

PlutoniumBytes · April 23, 2019, 8:53am

Hi,

i recently had this issue on my android device ( Moto Z2 ):
04-23 10:49:32.513 19263 19289 I trace : Main.hx:37: time(NULL)=1556009372
04-23 10:49:32.513 19263 19289 I trace : Main.hx:38: Std.random(1000)=266
04-23 10:49:32.513 19263 19289 I trace : Main.hx:39: Math.random()=0.647641502087936
…
04-23 10:49:54.143 19367 19393 I trace : Main.hx:37: time(NULL)=1556009394
04-23 10:49:54.143 19367 19393 I trace : Main.hx:38: Std.random(1000)=266
04-23 10:49:54.143 19367 19393 I trace : Main.hx:39: Math.random()=0.647641502087936

This happend only in one of my apps, so i tested a bit and found that <architecture name="arm64" /> caused it. Without that line, it works fine. I hope this will help

pozirk · April 23, 2019, 1:53pm

Oh shoot!
Thanks a lot @PlutoniumBytes!
Make sense, I have started releasing x64 version recently, but I can’t test it myself.

pozirk · April 24, 2019, 4:51pm

Hey @PlutoniumBytes, can you try this version of Random, if it works correctly on ARM64?

github.com

Kode/Kha/blob/master/Sources/kha/math/Random.hx

package kha.math;

//
// Random number generator
//
// Please use this one instead of the native Haxe one to
// keep consistency between different platforms.
//

// Mersenne twister
class Random {
	public function new(seed: Int): Void {
		MT = new Array<Int>();
		MT[624 - 1] = 0;
		MT[0] = seed;
		for (i in 1...624) MT[i] = 0x6c078965 * (MT[i - 1] ^ (MT[i - 1] >> 30)) + i;
	}
	
	public function Get(): Int {
		if (index == 0) GenerateNumbers();

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Thank you!

PlutoniumBytes · April 25, 2019, 7:56am

Works fine on ARM64

pozirk · April 25, 2019, 3:46pm

Thanks a lot!
…

andrew911 · January 26, 2021, 5:44pm

Stuck with same issue, after some tries found out that for ARM64 instead of srand -> srand48 should be used.

Could you verify?