forums.ps2dev.org

[Ghoti]

Hi folks,

i now use this code to random get some numbers:

[Garak]

Hi,

There is probably a better solution than this, but alas this is the solution I used and it did/does work.

I created the following function:

void InitRandomNumberGen()
{
int x;
struct timeval cTime;
gettimeofday(&cTime, 0);
int seed = cTime.tv_sec % 256;
for (x=0; x < seed; x++)
rand();
}

Call this function 1 time near the start of your program. It will get the system times and modulo it to get a number between 0 and 255. Then it calls the random number generator that many times. This will ensure the first random number actually used in your program is not the same random number allways returned first by the rand() function.

As you probably figured out, the random number generator allways produces the same random numbers. Doesn't sound very random but that's the way it usually works. I think normally a seed function that uses the system time (such as the one I mention above) is included in the random number function. I was suprised the one in the PSP lib did not plant a seed based on system time for you. But if you do it yourself as described above, you will get the results you are looking for.


Garak

[Raphael]

include <psputils.h> in your program and try the following

SceKernelUtilsMt19937Context ctx;
sceKernelUtilsMt19937Init(&ctx, time(NULL));

u32 rand_val = sceKernelUtilsMt19937UInt(&ctx);

the last statement should give you a random number everytime.

[Jim]

->Garak. That will give 256 different start points, which is better, but not as good as calling
srand(time(NULL));
which gives RAND_MAX+1 starting points.
Jim
_________________
http://www.dbfinteractive.com

[Garak]

srand(time(NULL)),

Yea that's hot... that's hot. I'll be sure to update my code and use it. Thanks.

Garak

[Saotome]

[Ghoti]

Hi folks,

If i am correct the function Raphael gave me was the best one right?
So it gives a number between? i mean i only have to get a 1 or a 2 randomized. like a boolean value :)
_________________
My PSP games:

Boxy II: http://www.ghoti.nl/boxyii.php
Elementals: http://www.ghoti.nl/Elementals.php

[Raphael]

/**
* Function to return a new psuedo random number.
*
* @param ctx - Pointer to a pre-initialised context.
* @return A pseudo random number (between 0 and MAX_INT).
*/
u32 sceKernelUtilsMt19937UInt(SceKernelUtilsMt19937Context *ctx);

So the function returns a complete random value inside the u32 valuespace.
So you could just use your get_random function and replace the rand() with the mersenne twister function and it would work perfectly. Just make the context global and initialise it at the start of your program.
Or in your special case, you'd just append

rand_val = 1 + rand_val % 2;

to my code snippet.

[Ghoti]

Hi,

Thanks that did the trick :) now my items come out all randomized and nice :)thank you!
_________________
My PSP games:

Boxy II: http://www.ghoti.nl/boxyii.php
Elementals: http://www.ghoti.nl/Elementals.php

[Ghoti]

Hi folks,

i use:

[Saotome]

what does empty mean?

your function:

[Ghoti]

Well i do this to draw:

[CyberBill]

You need to be a little more specific with the way you're drawing text & what sBuffer is.

Please post the code that calls the get_random() function and we can help you figure out whats wrong, because the get_random() function looks correct to me.

[Hexstr]

Hrmm, well I guess the get_random function is correct but if you are going to use it like it is defined you may want to replace the 1 and 2 with lo and hi. Like this

[BlackDiamond]

[waterbottle]

what include is needed to use time(NULL);?

I get the error

./main.cpp: In function 'int main(int, char**)':
./main.cpp:101: error: 'time' was not declared in this scope

when I use it..

[Kojima]

Is there a floating point random number generator in the psp sdk? (you know like on windows, where it returns between 0 and 1 and you just scale it into range yourself)

[siberianstar]

dunno if there is one in the sdk,

float __randf()
{
const int max = 1024;
return (float)(rand()%max)/max;
}

very simple,
note that i've wrote it here and i didn't try it.

[Kojima]

thanks, figured i could do it that way, just wondering if there was a fast build in func.

[Saotome]

you can do it like this

[Raphael]

[siberianstar]

[Raphael]

[siberianstar]

using Mersenne Twister for __randf_1, __randf2:

[Raphael]

[siberianstar]

yep, srand is much faster

[Jim]

Every 624 calls to mtrand, it has to go off and update the RNG's state, which is 624 32bit integers. The code for doing a single mtrandom number is normally just a handful of xors, shifts and ands.

The C99 standard recommends this implementation for rand()

[Raphael]