random generators new ways and old ways

[I C everything]

Hi
I have searched and found how you do it with rand function and mod
IDE also suggests _FRND
there is also mersienne twister and others
whats the best for a quiz?
not want end up with a repeative random generator or exactly the same quiz

M

[flp1969]

There are, at least, 2 dozens of "good" PRNGs out there (see here). There is no PRNGs truly random (the P stands for PSEUDO), but the quality of the randomness is pretty close to "random" as one's can get.

And lack of repetition is not a criteria for the "best" quality of randomness. Take a coin toss as an example: You have only 2 possible values and they will repeat a lot, it doesn't mean the set isn't random... Same thing as D6 dice toss...

If you want a "real' random generator for computers you'll need an external source of entropy (and luckly, Intel and AMD processors has an "internal" external source - hehe -- using RDRAND instruction or _rdrand??_step() function you'll get random BITS sequences).

My preference, due to simplicity and speed are, for PRNGs, LCG and xorshift128+.

If you don't care about speed and want to get a "truly" random values, in Linux/BSD/OSX you can do:

#include <fcntl.h>
#include <unistd.h>

// Assume /dev/urandom is always readable and we have enough
// file descriptors left... Should test this claims before using
// the routine.
unsigned int getUint32Random( void )
{
  unsigned int v;
  int fd;

  // /dev/random and /dev/urandom, nowadays, uses rdrand on
  // Intel and AMD platforms... It's not garantee it is truly
  // random in all Unixes, but the kernel tries to garantee a
  // flow of random bits.
  //
  // You can use /dev/random, but this other device will
  // try to garantee entropy (and could block from time to time).
  fd = open( "/dev/urandom", O_RDONLY );
  read( fd, &v, sizeof v );
  close( fd );

  return v;
}

[I C everything]

thanks flp1969

[laserlight]

It's not garantee it is truly random in all Unixes, but the kernel tries to garantee a flow of random bits.

I'd say /dev/urandom is guaranteed not to be "truly random" by design parameters, but that generally doesn't matter since a cryptographically secure PRNG seeded with sufficient entropy should be practically indistinguishable from a "truly random" source, whether it is used as a fallback or as an integral part of the system.

[I C everything]

thanks Laserlight

it seems to work good now produce random facts

[I C everything]

Next step: random generator that generates same seed= same world?

[I C everything]

//maybe this work
/////////////////////////////////////////////
//srand and rand in a feedback loop,starting with srand(1) or start with a big number
while (finished==true){
R=Rand();
srand(R);
x=R%numberofrandoms;
drawsomething(x);
if screenfilled()==1 {
finished=True;
}
}

[flp1969]

This will create the SAME sequence every time... it is NOT random or "psedo" random.

//maybe this work
/////////////////////////////////////////////
//srand and rand in a feedback loop,starting with srand(1) or start with a big number
while (finished==true){
R=Rand();
srand(R);
x=R%numberofrandoms;
drawsomething(x);
if screenfilled()==1 {
finished=True;
}
}

[I C everything]

this purpose is to generate lots of trees for a forest,buildings and such on a map until its filled,so you always endup with same