C++ random with seed

cocos2d-x C++
#1

Hi! Good day,

Why is it random() returns different value on android and iOS with both same value of seed.

I made it in this way…

// set my seed value
srand(p_seed);

// then call random()
for( int i = 0; i < 10; i++ )
{
random()
}

The weird thing is… android returns same pattern. (which is correct). but on iOS, different patterns printed every run. O_O’ Do you guys have any idea? by the way Im running this on an iPhone5 and nexus7 device.

Thanks!

aries

#2

Maybe the random algorithms are different. You can implement new one by yourself.


#3

Hi!

you mean to say… different device platforms have different pseudo random implementation? D: and the link is kinda geek link O_O (The randomized_algorithm one).

Thanks BTW!

aries

#4

Yes:)

#5

FYI…

The purpose of random with seed for me is… for easy generating same random integers on different platforms.

#6

You can try arc4random()

I’ve been using it on a game and it seems to work nicely.

#7

Hi Lance,

arc4random() uses the current time as its seed (I think?). so maybe not applicable.

Thanks anyway :smiley:

#8

or it seeds it self? please correct me if I sounds wrong. I am willing to learn things :smiley:

#9

Hi, I’m using this class for generating random numbers since our app has multiplayer support on all platforms and consistent pseudo random numbers are very important:

Based on Java’s LinearRandom pseudo random number implementation

class Random
{
public:
    Random(void);
    Random( long seed);
    static void setSeed(long _seed);
    static int next();
public:
    static long seed;
    static long multiplier;
    static long addend;
    static long mask;
};

long Random::multiplier = 0x5DEECE6C;
long Random::addend = 0xB;
long Random::mask = (1L << 48) - 1;
long Random::seed= 0x2342dda;   

Random::Random(void)
{
    setSeed(time(NULL));
}

Random::Random( long seed) {
    setSeed(seed);
}

void Random::setSeed(long _seed) {
    seed = (unsigned)(_seed & 0x7fffffffU);
}

int Random::next() {
    seed = (seed * 1103515245U + 12345U) & 0x7fffffffU;
    return (int)(seed);
}

usage:

#define RANDOM(X) Random::next()%(int)X
#define RANDOM_SEED(X) Random::setSeed(X)


RANDOM(100); // random number between 0 and 99

Hope this helps

2 Likes
#10

Oh wow! that is what Im absolutely looking for :smiley:

Thanks alot Cristian