#!/usr/bin/perl

###############################################
#                                             #
# This is just a simple cgi programme in perl #
# for showing large numbers written out.      #
#                                             #
# programmed by:                              #
# Wolfgang Hartmut Nitsche                    #
# http://nitsche.mobi                         #
# http://www.stanford.edu/~nitsche/           #
#                                             #
############################################### 


$query = $ENV{'QUERY_STRING'};
$filename = $ENV{'SCRIPT_FILENAME'};
$url = $ENV{'SCRIPT_URI'};


if($query eq 'source'){$what='source';}
elsif($query eq 'style'){$what='style';}
elsif($query eq 'hundred'){$what='hundred';}
elsif($query eq '1891plex'){$what='1891plex';}
elsif($query eq 'megaplex'){$what='megaplex';}
elsif($query eq 'googol'){$what='googol';}
elsif($query eq 'googolplex'){$what='googolplex';}
else{$what='mainpage';}


if($what eq 'source')
 {
  print "Content-type: text/plain\n\n";
  open(FILE, "<$filename");
  while(<FILE>)
   {
    print $_;
   }
  close(FILE);
 }


if($what eq 'style')
 {
  print "Content-type: text/css\n\n";
  print "\n";
  print 'body { background-color:#d6ddd3; color:#000000; }';
  print "\n";
  print 'a { text-decoration:underline; color:#0000ff; }';
  print "\n";
  print 'a:visited { color:#660099; }';
  print "\n";
  print 'a:hover { background:#ffff00; }';
  print "\n";
  print 'a:active {color:#ff0000; background:#ffffcc; }';
  print "\n";
  print '';
 }


if($what eq 'mainpage')
 {
  $title = "Googolplex and other large numbers written out (Start Page)";
  &htmlstart;

  print "\n";
  print '<p>Please choose which number you want to see written out</p>';
  print "\n";
  print '<ul>';
  print "\n";

  print '<li><a href="';
  print $url;
  print '?hundred">Hundred written out</a></li>';
  print "\n";

  print '<li><a href="';
  print $url;
  print '?googol">Googol written out</a></li>';
  print "\n";

  print '<li><a href="';
  print $url;
  print '?1891plex">1891plex written out</a></li>';
  print "\n";

  print '<li><a href="';
  print $url;
  print '?megaplex">Megaplex written out</a></li>';
  print "\n";

  print '<li><a href="';
  print $url;
  print '?googolplex">Googolplex written out</a></li>';
  print "\n";

  print '</ul>';
  print "\n";

  &htmlend;
 }


if($what eq 'hundred')
 {
  $numbername = "Hundred";
  $shownumber=1;
  $exponentmultiplier=2;
  $exponentzeros=0;
 }

if($what eq 'googol')
 {
  $numbername = "Googol";
  $shownumber=1;
  $exponentmultiplier=1;
  $exponentzeros=2;
 }

if($what eq '1891plex')
 {
  $numbername = "1891plex";
  $shownumber=1;
  $exponentmultiplier=1891;
  $exponentzeros=0;
 }

if($what eq 'megaplex')
 {
  $numbername = "Megaplex";
  $shownumber=1;
  $exponentmultiplier=1;
  $exponentzeros=6;
 }

if($what eq 'googolplex')
 {
  $numbername = "Googolplex";
  $shownumber=1;
  $exponentmultiplier=1;
  $exponentzeros=100;
 }


if($shownumber==1)
 {
  $title = "$numbername written out";
  &htmlstart;

  print "\n";
  print '<hr>';
  print "\n";
  print '<p><a href="';
  print $url;
  print '">Back to start page for large numbers written out</a></p>';
  print "\n";
  print '<hr>';
  print "\n";

  print "\n";
  print '1 ';
  print $numbername;
  print ' =<br>';
  print "\n";
  print '= 10^(';
  print $exponentmultiplier;
  print '*(10^';
  print $exponentzeros;
  print ')) =<br>';
  print "\n";

  $remainingexponentzeros = $exponentzeros;
  $exponent = $exponentmultiplier;
  while($remainingexponentzeros>0)
   {
    $exponent=$exponent.'0';
    $remainingexponentzeros--;
   }

  print "\n";
  print '= 10^';
  print $exponent;
  print ' =<br>';
  print "\n";

  print '= 1';
  $zerosshown = 0;

  $firstzeros = (substr $exponent, -1, 1);
  while($zerosshown<$firstzeros)
   {
    print '0';
    $zerosshown++;
   }
  print " \n";

  # (Now I know that the remaining number of zeros which
  # we still have to display is a multiple of 10.)

  while($zerosshown ne $exponent)
   {
    print " 0000000000 ";
    &increasezerosshownbyten;

    print '<!-- $zerosshown=';
    print $zerosshown;
    print ' ; $exponent=';
    print $exponent;
    print ' -->';
    print "\n";

   }

  print "\n";
  print '<hr>';
  print "\n";
  print '<p><a href="';
  print $url;
  print '">Back to start page for large numbers written out</a></p>';
  print "\n";


  &htmlend;
 }



sub htmlstart
 {
  print "Content-type: text/html\n\n";
  print "\n";
  print '<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">';
  print "\n";
  print '<html>';
  print "\n";
  print '<head>';
  print "\n";
  print '<title>';
  print $title;
  print '</title>';
  print "\n";
  print '<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">';
  print "\n";
  print '<link rel="stylesheet" href="';
  print "$url";
  print '?style" type="text/css">';
  print "\n";
  print '<base target="_top">';
  print "\n";
  print '</head>';
  print "\n";
  print '<body>';
  print "\n";
  print '<h1>';
  print $title;
  print '</h1>';
  print "\n";
  print '';
 }


sub htmlend
 {
  print "\n";
  print '<p>You can <a href="';
  print $url;
  print '?source">download the source</a> of the Perl-script ';
  print "\n";
  print 'which generates this and the other HTML pages ';
  print "\n";
  print 'about large numbers written out.</p>';
  print "\n";
  print '<p>This script has been written by Wolfgang H Nitsche ';
  print "\n";
  print '&lt;<a href="http://nitsche.mobi">http://nitsche.mobi</a>&gt; ';
  print "\n";
  print '&lt;<a href="http://www.stanford.edu/~nitsche/">http://www.stanford.edu/~nitsche/</a>&gt;.';
  print "\n";
  print '</p>';
  print "\n";
  print '</body>';
  print "\n";
  print '</html>';
  print "\n";
  print '';
 }



sub increasezerosshownbyten
 {
  # essentially, I want to implement
  # something like $zerosshown+=10 which works
  # for numbers with 100 digits
  $zerosshown = '0'.$zerosshown;
  @digits = split(//, $zerosshown);
  $digits[-2]+=1;
  for($i=$#digits; $i>=0; $i--)
   {
    if(10==$digits[$i])
     {
      $digits[$i] = 0;
      $digits[$i-1]++;
     }
   }
  if(0==$digits[0])
   {
    shift(@digits);
   }
  $zerosshown = join('', @digits);
 }


#######
#     #
# END #
#     #
#######