From: Bob Stout 

On Sat, 22 May 2004, Bruce D. Wedding wrote:

> Just my .02 cents.  I'm here to talk about C programming.  It seems to
> me we have like 5 or so active participants.  I don't guess I even
> understand the need.  Let's talk C.  Anyone know any published
> statistics on the MSVC standard library rand() function?

TTBOMK, it hasn't changed since the days of MSC 4.0. If that's true, it's
pretty good, but, IIRC, it could be improved by some of the versions in
SNIPPETS. It's not even that hard to test, though. Building a timed test
case using the built-in rand() and randomize() functions could be done
quite easily using the functions in SNIPPETS, e.g...

----[ snip ]----
/*
**  RANDTEST.C - Public domain demo by Bob Stout
**
**  Simple test for your compiler's rand() function.
**  Allows the user to specify the seed value and timeout on the command line.
**  Returns number of samples analyzed, arithmetic mean, and standard
**    deviation.
**  Searching for repeated patterns is left as an exercise for the user.
**
**  Compile and link with the following SNIPPETS functions:
**    mathstat.c
**    binsrch.c   (used by mathstat.c)
**    commafmt.c
**    commflt.c
**    strrev.c    (only required for gcc)
**
**  SNIPPETS headers required in addition to the obvious ones below:
**    sniptype.h  (used everywhere)
**    binsrch.h   (used by mathstat.h)
**    round.h     (used by numcnvrt.h)
**    pi.h        (used by numcnvrt.h)
**    snip_str.h  (only required for gcc)
*/

#include 
#include 
#include 
#include 
#include "mathstat.h"
#include "numcnvrt.h"

int main(int argc, char *argv[])
{
      unsigned seed = 37;           // Randomizing seed - primes are better
      double   timeout = 120.0;     // Test time in seconds
      time_t   t0;                  // Start time
      Stat_T   data;                // Collect statistics here
      size_t   N;                   // Sample counter
      char     numbuf[16];          // Used by commafmt()

      switch (argc)
      {
      case 3:
            timeout = strtod(argv[2], NULL);

      case 2:
            seed = (int)strtol(argv[1], NULL, 16);

      case 1:
            break;

      default:
            puts("Usage: RANDTEST [seed] | [seed timeout (secs)]");
            return EXIT_FAILURE;
      }

      stat_init(&data, 0);
      srand(seed);

      fprintf(stderr, "Working");
      for (t0 = time(NULL); (difftime(time(NULL), t0) < timeout) ||
                (UINT_MAX == N); )
      {
            int datum = rand();

            stat_add((double)datum, &data);
            N = stat_count(&data);


/***************************************************************/
/*                                                             */
/*  If desired, put code here to detect repeated sequences.    */
/*                                                             */
/***************************************************************/

            /*
            ** Provide periodic feedback to let 'em know we're not dead
            */

            if (0 == (N % 1000))
            {
                  fputc('.', stderr);
                  fflush(sterr);
            }
      }

      commafmt(numbuf, 16, N);
      printf("\n\nRANDTEST done (%s samples)\n", numbuf);
      comma_float(stat_mean(&data), numbuf, 4);
      printf(" mean                     = %s\n", numbuf);
      comma_float(stat_stddevP(&data), numbuf, 4);
      printf(" standard deviation       = %s\n", numbuf);

      return EXIT_SUCCESS;
}
----[ snip ]----

Oddly enough, I wasn't able to get it working with MSVC (I recently
reinstalled everything and something's wrong in my setup). However, I did
run quick tests with the Digital Mars (nee Symantec, nee Zortech) compiler
and the MinGW32 port of gcc. Results follow:

----[ snip - DMC output ]----
RANDTEST done (10,752,906 samples)
 mean                     = 16,386.4825
 standard deviation       = 7,736,876.6551
----[ snip - GCC output ]----
RANDTEST done (2,163,615 samples)
 mean                     = 16,384.2081
 standard deviation       = 323,139.8046
----[ snip ]----

Obviously, quite crude and of dubious value, but a potentially useful starting point.

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