/* File: random.c */

/*
 *********************************************************************
   ALTERNATING BIT AND GO-BACK-N NETWORK EMULATOR

   Revised version of code by J.F. Kurose

   From the companion website for 
   _Computer Networking: A Top-Down Approach Featuring the Internet_
   by J.F. Kurose and K. W. Ross
   (c) 2001 by Addison Wesley Longman

   Based on document at <URL:http://occawlonline.pearsoned.com/
   bookbind/pubbooks/kurose-ross1/chapter4/custom12/deluxe-content.html>
   (as of 02 July 2002)
 *********************************************************************
*/

/************** PSEUDORANDOM NUMBERS ******************/
/*  The next set of routines deal with random numbers */
/******************************************************/
 
/*------------*/
/* test_rand  */
/*            *----------------------------------------------------*/
/*                                                                 */
/*-----------------------------------------------------------------*/
void test_rand(void){
  int i;
  float sum;
  float avg;
  
 #define RANDOM
 #ifdef RANDOM
   srand((unsigned int)time((time_t *)NULL));
 #else
   srand(42);    /* same simulation every time */
 #endif
   /* test random number generator for students */
   sum = 0.0;
   for (i=0; i<1000; i++) {
     sum += jimsrand(); /* jimsrand() should be uniform in [0,1] */
   }
   avg = sum/1000.0;
   if (TRACE > 3) {
     printf("%*sTEST_RAND: sum = %f, avg == %f\n\n",INDENT,"", sum, avg);
   }
   if (avg < 0.25 || avg > 0.75) {
     printf("\n\n**SIMULATION HALTED**\n");
     printf("It is likely that random number generation on your machine\n");
     printf("is different from what this emulator expects.  Please read\n");
     printf("the jimsrand() function in the emulator code. Sorry.      \n");
     if (TRACE) {
       printf("%*sTEST_RAND: using rand() with ", INDENT, "");
       #ifdef RANDOM
         printf("random");
       #else
         printf("constant");
       #endif
       printf(" seed\n");
       printf("%*sTEST_RAND: sum = %f, avg == %f\n",INDENT,"", sum, avg);
     }
     exit(EXIT_FAILURE);
   } 
} /* test_rand() */


/*------------*/
/* jimsrand  */
/*            *----------------------------------------------------*/
/*                                                                 */
/*  Return a float in range [0,1].                                 */
/*-----------------------------------------------------------------*/
float
jimsrand(void) {
  return ((float)rand())/RAND_MAX;
} /* jimsrand() */

/* EOF (random.c) */