-5 ..   -1  [   1] #
   0 ..    4  [   7] #######
   5 ..    9  [   6] ######
  10 ..   14  [   7] #######
  15 ..   19  [   3] ###
  20 ..   24  [   1] #
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sub show_histogram
{
   # Prints a simple text histogram given a reference
   # to an array of integers.
   # Larry Leszczynski <larryl@furph.com>

   my ($array_ref, $binsize, $width) = @_;
   $binsize ||= 1;
   $width   ||= 50;

   use POSIX qw(ceil floor);

   # Divide input data into bins:
   my %bin_count = ();   # number of items in each bin
   foreach ( @$array_ref ) {
      my $bin = floor(($_+.5)/$binsize);
      $bin_count{$bin}++;
   }

   my $max_items = 0;   # maximum items in a single bin
   foreach ( values %bin_count ) {
      $max_items = $_ if $_ > $max_items;
   }

   # Try to keep histogram on one page width:
   my $scale = 1;
   if ( $max_items > $width ) {
      if ( $max_items <= ($width*5) ) {
         $scale = 5;
      }
      else {
         while ( ($max_items/$scale) > $width ) {
            $scale *= 10;
         }
      }
   }

   my @bins   = sort {$a <=> $b} keys %bin_count;
   my $bin    = $bins[0];    # lowest value bin
   my $maxbin = $bins[-1];   # highest value bin

   my $binfmt_width = ( length $maxbin > length $bin )
                      ? length $maxbin : length $bin;
   my $cntfmt_width = length $max_items;

   my $start = $bin * $binsize;
   my $end   = $start + $binsize - 1;
   do {
      my $count = $bin_count{$bin} || 0;
      my $extra = ( $count % $scale ) ? '.' : '';
      printf "%*d .. %*d  \[%*d\] %s$extra\n",
                    $binfmt_width, $start,
                    $binfmt_width, $end,
                    $cntfmt_width, $count,
                    '#' x ceil($count/$scale);
      $start += $binsize;
      $end   += $binsize;
   } while ( $bin++ < $maxbin );
   print "\n  Scale: #=$scale\n" if $scale > 1;
}
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