eval "exec nice -19 perl $0 $*"
       if $running_under_some_shell;
# --------------------------------------------------------------------
+-------
# pi.perl  computes pi (3.14...) about 5120 Digits
#
# W. Kebsch, July-1988  {uunet!mcvax}!unido!nixpbe!kebsch

$my_name = `basename $0`; chop($my_name);
$version = $my_name . "-1.2";

# some working parameter

$smax =  5120;          # max digits
$lmax =     4;          # digits per one array element
$hmax = 10000;          # one array element contains: 0..9999
$smin = $lmax;          # min digits
$mag  =     7;          # magic number

# subroutines

sub mul_tm              # multiply the tm array with a long value
{
   $cb = pop(@_);      # elements(array)
   $x  = pop(@_);      # value

   $c = 0;
   for($i = 1; $i <= $cb; $i++)
   {
       $z      = $tm[$i] * $x + $c;
       $c      = int($z / $hmax);
       $tm[$i] = $z - $c * $hmax;
   }
}

sub mul_pm              # multiply the pm array with a long value
{
   $cb = pop(@_);      # elements(array)
   $x  = pop(@_);      # value

   $c = 0;
   for($i = 1; $i <= $cb; $i++)
   {
       $z      = $pm[$i] * $x + $c;
       $c      = int($z / $hmax);
       $pm[$i] = $z - $c * $hmax;
   }
}

sub divide              # divide the tm array by a long value
{
   $cb = pop(@_);      # elements(array)
   $x  = pop(@_);      # value

   $c = 0;
   for($i = $cb; $i >= 1; $i--)
   {
       $z      = $tm[$i] + $c;
       $q      = int($z / $x);
       $tm[$i] = $q;
       $c      = ($z - $q * $x) * $hmax;
   }
}

sub add                 # add tm array to pm array

{
   $cb = pop(@_);      # elements(array)

   $c = 0;
   for($i = 1; $i <= $cb; $i++)
   {
       $z = $pm[$i] + $tm[$i] + $c;
       if($z >= $hmax)
       {
           $pm[$i] = $z - $hmax;
           $c      = 1;
       }
       else
       {
           $pm[$i] = $z;
           $c      = 0;
       }
   }
}

$m0 = 0; $m1 = 0; $m2 = 0;

sub check_xb            # reduce current no. of elements (speed up!)
{
   $cb = pop(@_);      # current no. of elements

   if(($pm[$cb] == $m0) && ($pm[$cb - 1] == $m1) && ($pm[$cb - 2] == $
+m2))
   {
       $cb--;
   }
   $m0 = $pm[$cb];
   $m1 = $pm[$cb - 1];
   $m2 = $pm[$cb - 2];
   $cb;
}

sub display             # show the result
{
   $cb = pop(@_);      # elements(array);

   printf("\n%3d.", $pm[$cb]);
   $j = $mag - $lmax;
   for($i = $cb - 1; $i >= $j; $i--)
   {
       printf(" %04d", $pm[$i]);
   }
   print "\n";
}

sub the_job             # let's do the job
{
   $s = pop(@_);       # no. of digits

   $s  = int(($s + $lmax - 1) / $lmax) * $lmax;
   $b  = int($s / $lmax) + $mag - $lmax;
   $xb = $b;
   $t  = int($s * 5 / 3);

   for($i = 1; $i <= $b; $i++)         # init arrays
   {
       $pm[$i] = 0;
       $tm[$i] = 0;
   }
   $pm[$b - 1] = $hmax / 2;
   $tm[$b - 1] = $hmax / 2;

   printf("digits:%5d, terms:%5d, elements:%5d\n", $s, $t, $b);
   for($n = 1; $n <= $t; $n++)
   {
       printf("\r\t\t\t  term:%5d", $n);
       if($n < 200)
       {
           do mul_tm((4 * ($n * $n - $n) + 1), $xb);
       }
       else
       {
           do mul_tm((2 * $n - 1), $xb);
           do mul_tm((2 * $n - 1), $xb);
       }
       if($n < 100)
       {
           do divide(($n * (16 * $n + 8)), $xb);
       }
       else

       {
           do divide((8 * $n), $xb);
           do divide((2 * $n + 1), $xb);
       }
       do add($xb);
       if($xb > $mag)
       {
           $xb = do check_xb($xb);
       }
   }
   do mul_pm(6, $b);
   do display($b);
   ($user,$sys,$cuser,$csys) = times;
   printf("\n[u=%g  s=%g  cu=%g  cs=%g]\n",$user, $sys, $cuser, $csys)
+;
}

# main block ---------------------------------------------------------
+-------

$no_of_args = $#ARGV + 1;
print("$version, ");
die("usage: $my_name <no. of digits>") unless($no_of_args == 1);
$digits = int($ARGV[0]);
die("no. of digits out of range [$smin\..$smax]")
                           unless(($digits >= $smin) && ($digits <= $s
+max));
do the_job($digits);
exit 0;

# That's all ---------------------------------------------------------
+-------
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