[Tfug] /dev/random

[Charles R Kiss]

I stole the following code:

#include <iostream>
#include <fstream>
#include <cstdlib>


    using namespace std;

    //const char *rand_device = "/dev/urandom";
    const char *rand_device = "/dev/random";

    int
    main() {
      int getuid();


      cout << "uid " << getuid() << endl;
      std::ifstream random(rand_device);
      if (!random) {
        perror(rand_device);
        return 1;
      }

      unsigned int seed;
      random.read((char*)&seed, sizeof(seed));
      cout << "seed: " << seed << endl;
      return 0;
    }



from here:

http://groups-beta.google.com/group/comp.lang.c++.moderated/browse_thread/thread/3585188f84021b65 


but when compiling:     charles at house:~/game$ g++ t.C -o t

I get the following error:

t.C: In function `int main()':
t.C:18: implicit declaration of function `int perror(...)'

Why?  I tried adding the <stdio>  directive; but that didn't help.  But 
I did find this in /usr/include/stio.h

/* Print a message describing the meaning of the value of errno.  */
extern void perror (__const char *__s) __THROW;


The above code when simplified to:

#include <iostream>
#include <fstream>
#include <cstdlib>


    using namespace std;

    //const char *rand_device = "/dev/urandom";
    const char *rand_device = "/dev/random";

    int
    main() {

      std::ifstream random(rand_device);


      unsigned int seed;
      random.read((char*)&seed, sizeof(seed));
      cout << "seed: " << seed << endl;
      return 0;
    }

generates random numbers quickly, but I guess I'm feeling like I'm 
missing a check on the entropy pool (something I don't yet understand); 
but I haven't figured that out yet, I'm just guessing.   How fast and 
for how long can I generate these numbers; which are rather large.

Is there a way of limiting the random numbers output to three or four 
numbers numbers without using the modulus function?   Say, reading 
straight off a 2-bit byte random stream, or a 3-bit byte stream, or an 
n-bit byte stream?

For now, I just need fast zeros and ones randomly distributed; but most 
highly random.   Basically, super-fast, super-random, but only 0's and 
1's; then, later, I guess, not-so-fast, but just as random, values 
betwen 0 and 4 [is this possible, or is the randomness a function of the 
byte size??]; ie. controlling the size of the byte, then dumping the 
values into a array.   Just for fun, obviously I have much more reading 
to do.

Also, is controlling the entropy pool, as in BSD's rndcontrol function, 
possible?  Or do I just throw the processor with keyboard and mouse down 
the stairs while it's computing?

Thanks in advance,

Charles

ps.  I joined the dclug here; but it just won't be the same  :( .   
 Especially the outdoor air temperature, which should normally feel 
below 127F.