C - random number generator - Tilted Forum Project Discussion Community

supafly · 01-26-2004, 09:25 AM

I'am looking for a random number generator using the C language wich can generate 100 random ints. The ints must be stored in an array.

Can anyone help me?

dimbulb · 01-26-2004, 09:35 AM

Here is a state of the art random number generator. Practically industrial strength. The output comes out in the form of a uniform random variable though, so if you need other probability distributions, you have to obtain them from the uniform variable in the usual way (check out simulation textbooks and resources if you need the 'recipes'). It is also not hard converting uniform r.v's into integers. just do a ceiling on the r.v.

Also, it only outputs a single number at a time, but I'm sure you can put it into an array yourself.

Check out the RngStream link from here....
http://www.iro.umontreal.ca/~simardr/

Here are the links to the C and C++ files themselves.
http://www.iro.umontreal.ca/~lecuyer/myftp/streams00/

dimbulb · 01-26-2004, 09:35 AM

oh... remember to credit the authors in your program. It would be stealing otherwise.

cheerios · 01-26-2004, 11:53 AM

why not just generate numbers w/ stdlib.h then put them into an array?

Quote:

RANDOM(3) BSD Library Functions Manual RANDOM(3)

NAME
random, srandom, srandomdev, initstate, setstate - better random number
generator; routines for changing generators

LIBRARY
Standard C Library (libc, -lc)

SYNOPSIS
#include <stdlib.h>

long
random(void);

void
srandom(unsigned long seed);

void
srandomdev(void);

char *
initstate(unsigned long seed, char *state, long n);

char *
setstate(char *state);

DESCRIPTION
The random() function uses a non-linear additive feedback random number
generator employing a default table of size 31 long integers to return
successive pseudo-random numbers in the range from 0 to (2**31)-1. The
period of this random number generator is very large, approximately
16*((2**31)-1).

The random() and srandom() functions have (almost) the same calling
sequence and initialization properties as the rand(3) and srand(3) func-
tions. The difference is that rand(3) produces a much less random
sequence -- in fact, the low dozen bits generated by rand go through a
cyclic pattern. All the bits generated by random() are usable. For
example, `random()&01' will produce a random binary value.

Like rand(3), random() will by default produce a sequence of numbers that
can be duplicated by calling srandom() with `1' as the seed.

The srandomdev() routine initialize a state array using random(4) random
number device which returns good random numbers, suitable for crypto-
graphic use. Note that this particular seeding procedure can generate states which are impossible to reproduce by calling srandom() with any
value, since the succeeding terms in the state buffer are no longer
derived from the LC algorithm applied to a fixed seed.

The initstate() routine allows a state array, passed in as an argument,
to be initialized for future use. The size of the state array (in bytes)
is used by initstate() to decide how sophisticated a random number gener-
ator it should use -- the more state, the better the random numbers will
be. (Current "optimal" values for the amount of state information are 8,
32, 64, 128, and 256 bytes; other amounts will be rounded down to the
nearest known amount. Using less than 8 bytes will cause an error.) The
seed for the initialization (which specifies a starting point for the
random number sequence, and provides for restarting at the same point) is
also an argument. The initstate() function returns a pointer to the pre-
vious state information array.

Once a state has been initialized, the setstate() routine provides for
rapid switching between states. The setstate() function returns a
pointer to the previous state array; its argument state array is used for
further random number generation until the next call to initstate() or
setstate().

Once a state array has been initialized, it may be restarted at a differ-
ent point either by calling initstate() (with the desired seed, the state
array, and its size) or by calling both setstate() (with the state array)
and srandom() (with the desired seed). The advantage of calling both
setstate() and srandom() is that the size of the state array does not
have to be remembered after it is initialized.

With 256 bytes of state information, the period of the random number gen-
erator is greater than 2**69 which should be sufficient for most pur-
poses.

AUTHORS
Earl T. Cohen

that's "man random" on a BSD Unix system.

supafly · 01-27-2004, 05:06 AM

I'll try both your suggestions, thanks for your help. I'll let you know if if works.

pythonite · 01-27-2004, 06:10 PM

Be careful when using rand in c/c++... only generate the seed once! I'm sure there are tons of example code out there.

supafly · 01-28-2004, 07:22 AM

The rand command works!
Check out the source code:

#include <stdio.h>

#define MAX 100

int a[MAX];
int rand_seed=10;

/*Returns random number between 0 and 32767.*/

int rand()
{
rand_seed = rand_seed * 1103515245 +12345;
return (unsigned int)(rand_seed / 65536) % 32768;
}

int main()
{
int i,t,x,y;

/* fill array */
for (i=0; i < MAX; i++)
{
a[i]=rand();
printf("%d\n",a[i]);
}
return 0;
}

Comment:
#define MAX 100, the size of the array is 100.
int rand_seed=10, by changing the the value of the seed you will get an array with other random ganerated numbers.

Thank you all for helping me!

dnd · 02-01-2004, 07:03 AM

a thread on random number generators and no has mentioned that it is in reality only possible to create a pseudo random number!!! the pedantic of us must have missed this one!

Quadraton · 02-07-2004, 09:27 PM

Quote:

Originally posted by dnd
a thread on random number generators and no has mentioned that it is in reality only possible to create a pseudo random number!!! the pedantic of us must have missed this one!

Damn, I got to this thread late.

I was going to mention pseudo-random numbers. Really. I was

KnifeMissile · 02-07-2004, 10:33 PM

I was hoping no one would mention this.
I mean, if the guy doesn't even know how to generate numbers, pseudo-random or otherwise, how much can he really care about the distinction?

cheerios · 02-08-2004, 12:24 AM

dnd: I figured that was a given :shrug:

nothingx · 02-10-2004, 03:19 PM

Actually, if you wanna make a really badass random number generator you should throw in a little entropy. For example, instead of using your constants: 1103515245, 12345, & 65536, you could form a function based on current disk i/o, cpu usage, cpu temperature, fan speed, etc... A little bit of hardware randomness will get you closer to truely random.

CSflim · 02-12-2004, 01:56 PM

...what we REALLY need is a geiger counter and a radioactive isotope...

ummm, never mind.

Quadraton · 02-12-2004, 03:03 PM

Quote:

Originally posted by KnifeMissle
I was hoping no one would mention this.
I mean, if the guy doesn't even know how to generate numbers, pseudo-random or otherwise, how much can he really care about the distinction?

Point taken.

01-26-2004, 09:25 AM	#1 (permalink)
supafly Psycho Location: Rotterdam	C - random number generator I'am looking for a random number generator using the C language wich can generate 100 random ints. The ints must be stored in an array. Can anyone help me?

01-27-2004, 05:06 AM	#5 (permalink)
supafly Psycho Location: Rotterdam	I'll try both your suggestions, thanks for your help. I'll let you know if if works. __________________ Thumbs up

01-28-2004, 07:22 AM	#7 (permalink)
supafly Psycho Location: Rotterdam	The rand command works! Check out the source code: #include <stdio.h> #define MAX 100 int a[MAX]; int rand_seed=10; /Returns random number between 0 and 32767./ int rand() { rand_seed = rand_seed * 1103515245 +12345; return (unsigned int)(rand_seed / 65536) % 32768; } int main() { int i,t,x,y; /* fill array */ for (i=0; i < MAX; i++) { a[i]=rand(); printf("%d\n",a[i]); } return 0; } Comment: #define MAX 100, the size of the array is 100. int rand_seed=10, by changing the the value of the seed you will get an array with other random ganerated numbers. Thank you all for helping me! __________________ Thumbs up

02-01-2004, 07:03 AM	#8 (permalink)
dnd Psycho Location: London...no longer a student	a thread on random number generators and no has mentioned that it is in reality only possible to create a pseudo random number!!! the pedantic of us must have missed this one! __________________ "Never underestimate a dumb question"-- Brandon Boyd

02-12-2004, 01:56 PM	#13 (permalink)
CSflim Sky Piercer Location: Ireland	...what we REALLY need is a geiger counter and a radioactive isotope... ummm, never mind. __________________

01-26-2004, 09:35 AM	#2 (permalink)
dimbulb Riiiiight........	Here is a state of the art random number generator. Practically industrial strength. The output comes out in the form of a uniform random variable though, so if you need other probability distributions, you have to obtain them from the uniform variable in the usual way (check out simulation textbooks and resources if you need the 'recipes'). It is also not hard converting uniform r.v's into integers. just do a ceiling on the r.v. Also, it only outputs a single number at a time, but I'm sure you can put it into an array yourself. Check out the RngStream link from here.... http://www.iro.umontreal.ca/~simardr/ Here are the links to the C and C++ files themselves. http://www.iro.umontreal.ca/~lecuyer/myftp/streams00/

01-26-2004, 09:35 AM	#3 (permalink)
dimbulb Riiiiight........	oh... remember to credit the authors in your program. It would be stealing otherwise.

01-27-2004, 06:10 PM	#6 (permalink)
pythonite Upright Location: Chico, CA	Be careful when using rand in c/c++... only generate the seed once! I'm sure there are tons of example code out there.

02-07-2004, 10:33 PM	#10 (permalink)
KnifeMissile Location: Waterloo, Ontario	I was hoping no one would mention this. I mean, if the guy doesn't even know how to generate numbers, pseudo-random or otherwise, how much can he really care about the distinction?

02-08-2004, 12:24 AM	#11 (permalink)
cheerios Banned Location: 'bout 2 feet from my iMac	dnd: I figured that was a given :shrug:

02-10-2004, 03:19 PM	#12 (permalink)
nothingx undead Location: nihilistic freedom	Actually, if you wanna make a really badass random number generator you should throw in a little entropy. For example, instead of using your constants: 1103515245, 12345, & 65536, you could form a function based on current disk i/o, cpu usage, cpu temperature, fan speed, etc... A little bit of hardware randomness will get you closer to truely random.