Re: Hunt for rand and srand implementations ;)

From: Skybuck Flying (nospam_at_hotmail.com)
Date: 10/28/04 

Date: Thu, 28 Oct 2004 23:33:51 +0200

Ah... I found a way to reply to my own message with the buggy outlook
express ;)

( Go into the sent folder and then click reply all and remove yourself from
the CC :) hehehe )

Ok there was a little bug in my initial version... srand was being called
for the IBM version... but IBM_AIX_srand should ofcourse be called...

I have also added another platform... it's actually more an UNIX/POSIX api I
think... yes POSIX hehe... and the funny thing is IBM_AIX results are the
same for the POSIX results.... and unix,linux,solaris and some hp os-es
probably have the same srand() and rand() routines... I wonder if
redhat,debian, etc also have the same ones.. or different ones ?! ;)

Here is the code so far ;) (and I'll add to links for microsoft's doc for
visual c... I pasted the whole text in the source.. but I dont wanna paste
it here... so here goes :) )

// Hunt for random number generators ;)
// Started by Skybuck Flying on 28 october 2004 :)

// visual c cpp 6 srand and rand
// implementation unknown...
//
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vccore98/HTML/_crt_srand.asp
//
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vccore98/HTML/_crt_rand.asp

void visual_c_cpp_6_srand( unsigned int seed )
{
 srand( seed );
}

int visual_c_cpp_6_rand(void)
{
 return rand();
}

// IBM AIX srand and rand implementation occurding to:
//
http://publib.boulder.ibm.com/infocenter/pseries/index.jsp?topic=/com.ibm.aix.doc/libs/basetrf2/rand.htm
static unsigned int IBM_AIX_next = 1;

int IBM_AIX_rand(void)
{
 IBM_AIX_next = IBM_AIX_next * 1103515245 + 12345;
 return ((IBM_AIX_next >>16) & 32767);
}

void IBM_AIX_srand(unsigned int Seed)
{
 IBM_AIX_next = Seed;
}

// POSIX 1003.1-2003 gives the following example of an implementation of
// rand() and srand(), possibly useful when one needs the same sequence on
// two different machines.

// the following platforms probably use this random number generator:
// FreeBSD, Linux, Solaris, IBM-AIX, possible even more OS-es based on
UNIX/POSIX ;)

static unsigned long POSIX_next = 1;

/* RAND_MAX assumed to be 32767 */
int POSIX_rand(void)
{
 POSIX_next = POSIX_next * 1103515245 + 12345;
 return((unsigned)(POSIX_next/65536) % 32768);
}

void POSIX_srand(unsigned seed)
{
 POSIX_next = seed;
}

int main()
{
 int seed;

 // use same seed for all srand functions to find same implementations ;)
etc ;)
 seed = 12345;

 // visual c/c++ 6.0 srand and rand:
 printf("visual c/c++ 6.0 \n" );

 srand( seed );

 printf("rand1: %d \n", rand() );
 printf("rand2: %d \n", rand() );
 printf("rand3: %d \n", rand() );

 // visual c/c++ 6.0 rand output for srand seed 12345
 // rand1: 7584
 // rand2: 19164
 // rand3: 25795

 // IBM AIX srand and rand:
 printf("IBM AIX \n" );

 IBM_AIX_srand( seed );

 printf("rand1: %d \n", IBM_AIX_rand() );
 printf("rand2: %d \n", IBM_AIX_rand() );
 printf("rand3: %d \n", IBM_AIX_rand() );

 // IBM AIX rand output for srand seed 12345
 // rand1: 21468
 // rand2: 9988
 // rand3: 22117

 // POSIX srand and rand:
 printf("POSIX \n" );

 POSIX_srand( seed );

 printf("rand1: %d \n", POSIX_rand() );
 printf("rand2: %d \n", POSIX_rand() );
 printf("rand3: %d \n", POSIX_rand() );

 // POSIX rand output for srand seed 12345
 // rand1: 21468
 // rand2: 9988
 // rand3: 22117

 return 0;
}

Bye,
  Skybuck

Relevant Pages

  • Re: Hunt for rand and srand implementations ;)
    ... Also I tested knoppix's rand and srand.... ... rand and srand... ... void srand(unsigned int seed); ... rand retrieves the pseudorandom numbers that are generated. ...
    (sci.crypt)
  • Re: Floating point load-store behaviour.
    ... This should be "int main". ... calling srand(), you're interfering with the generator. ... You should call srand() exactly once, ...
    (comp.lang.c)
  • Re: rand and srand
    ... value from rand() by 2001, and returns the remainder - so the number can ... The C99 standard wants and int. ... automatic void of course with just as parameters. ... So is there really a need to use srand? ...
    (comp.lang.c)
  • Re: Random string
    ... The time between a call to srand() and a subsequent ... call to rand() makes no difference whatsoever unless 1) your ... int rand_lim{ ...
    (microsoft.public.vc.mfc)
  • Re: Way for computing random primes in standard C.
    ... randomness of the numbers returned by rand? ... call to srand() were removed (perhaps with a different number of ... the randomness is in the non-perfect algorithm ... ] sequence has some internal initial values. ...
    (comp.lang.c)