www.pudn.com > lpc.zip > random_i.c

/***********************************************************************
*
*	RANDOM Version 49
*
***********************************************************************
*
*  Pseudo random number generator based on Knuth, Vol 2, p. 27.
*
* Function Return:
*  RANDOM - Integer variable, uniformly distributed over -32768 to 32767
*
* Warning:  This routine contains statements which are specific to VAX Fortran.
*		I'll try it anyway - Tiner
*/

#define MIDTAP 1
#define MAXTAP 4

#include "ourstuff.h"

int_type Rrandom_i()
{
  int_type the_random;
  static int_type y[MAXTAP+1]={-21161, -8478, 30892,-10216, 16950};
  static int_type j=MIDTAP, k=MAXTAP;
  
  /*   The following is a 16 bit 2's complement addition,
   *   with overflow checking disabled	*/
  
  y[k] += y[j];
  
  /* to make 16 bit rollover to -/+ */
  /*
    if(y[k] > 32767) 
    y[k] = -(32768 - (y[k] & 32767));
    if(y[k] < -32768)
    y[k] = y[k] & 32767;
    */
  
  the_random = y[k];
  k--;
  if (k < 0) k = MAXTAP;
  j--;
  if (j < 0) j = MAXTAP;

  return(the_random);

}