SingleSource/Benchmarks/Misc/pi.c

/*--- pi.c       PROGRAM RANPI
 *
 *   Program to compute PI by probability.
 *   By Mark Riordan  24-DEC-1986; 
 *   Original version apparently by Don Shull.
 *   To be used as a CPU benchmark.
 *  
 *  Translated to C from FORTRAN 20 Nov 1993
 */
#include <stdio.h>

void myadd(float *sum,float *addend) {
/*
c   Simple adding subroutine thrown in to allow subroutine
c   calls/returns to be factored in as part of the benchmark.
*/
      *sum = *sum + *addend;
}


int main(int argc, char *argv[]) {
   float ztot, yran, ymult, ymod, x, y, z, pi, prod;
   long int low, ixran, itot, j, iprod;

      printf("Starting PI...\n");
      ztot = 0.0;
      low = 1;
      ixran = 1907;
      yran = 5813.0;
      ymult = 1307.0;
      ymod = 5471.0;
#ifdef SMALL_PROBLEM_SIZE
      itot = 4000000;
#else
      itot = 40000000;
#endif

      for(j=1; j<=itot; j++) {
/*
c   X and Y are two uniform random numbers between 0 and 1.
c   They are computed using two linear congruential generators.
c   A mix of integer and real arithmetic is used to simulate a
c   real program.  Magnitudes are kept small to prevent 32-bit
c   integer overflow and to allow full precision even with a 23-bit
c   mantissa.
*/

        iprod = 27611 * ixran;
        ixran = iprod - 74383*(long int)(iprod/74383);
        x = (float)ixran / 74383.0;
        prod = ymult * yran;
        yran = (prod - ymod*(long int)(prod/ymod));
        y = yran / ymod;
        z = x*x + y*y;
        myadd(&ztot,&z);
        if ( z <= 1.0 ) {
          low = low + 1;
        }
      }
      printf(" x = %9.6f    y = %12.2f  low = %8d j = %7d\n",x,y,(int)low,(int)j);
      pi = 4.0 * (float)low/(float)itot;
      printf("Pi = %9.6f ztot = %12.2f itot = %8d\n",pi,ztot*0.0,(int)itot);
      return 0;
}