Path: utzoo!attcan!uunet!olivea!apple!mips!hal!mark
From: mark@mips.COM (Mark G. Johnson)
Newsgroups: comp.benchmarks
Subject: (Useless)  X  (Meaningless)   {digits of PI}
Message-ID: <45469@mips.mips.COM>
Date: 1 Feb 91 22:50:24 GMT
Sender: news@mips.COM
Reply-To: mark@mips.COM (Mark G. Johnson)
Lines: 60


Here is an article that contains the cross-product of two allegedly
useless pursuits: (1) promulgating small CPU benchmarks; (2) calculating
digits of PI.

The C code posted by jroth@allvax.dec.com (Jim Roth) on 25 Jun 90
14:10:59 GMT was tried on a couple of machines.  This program
calculates the first 1000 decimal digits of PI.

Here are the meager benchmark measurements made to date (/bin/time):
   Sun     SPARCStation 1+        9.5 real     9.5 user     0.0 sys
   Sun     SPARCStation 2        29.4 real    29.3 user     0.0 sys <*** huh?
   MIPS    Magnum workstation     3.0 real     2.8 user     0.0 sys

Note the very anomalous result on SS-II; I tried the code on 3 different
machines and kept getting the same answer.  Replication/refutation of
this result would be much appreciated.

Speed of the IBM-POWER RISC wizzies on (computing digits of PI) would be
interesting to know, too; unfortunately I don't have one close to hand.

C code follows:
------------------------------------------------------------------------------

/*   Message-ID: <1902@ryn.esg.dec.com>     */
/*   Date:  25 Jun 90 14:10:59 GMT          */

/*  1000 digits of PI					    */
/*  'Spigot' algorithm origionally due to Stanly Rabinowitz */

#include <stdio.h>
#include <math.h>

main()
{
  long d = 4, r = 10000, n = 251, m = 3.322*n*d;
  long i, j, k, q;
  static long a[3340];

  for (i = 0; i <= m; i++) a[i] = 2;
  a[m] = 4;

  for (i = 1; i <= n; i++) {
    q = 0;
    for (k = m; k > 0; k--) {
      a[k] = a[k]*r+q;
      q = a[k]/(2*k+1);
      a[k] -= (2*k+1)*q;
      q *= k;
    }
    a[0] = a[0]*r+q;
    q = a[0]/r;
    a[0] -= q*r;
    printf("%04d%s", q, i & 7 ? "  " : "\n");
  }
}
-- 
 -- Mark Johnson	
 	MIPS Computer Systems, 930 E. Arques M/S 2-02, Sunnyvale, CA 94086
	(408) 524-8308    mark@mips.com  {or ...!decwrl!mips!mark}