# determine char entropy from file. by wufnik.

my $fil = shift;
open (FIL, $fil) || die ("no filfor entropy calc, $!");
my $filstr = do { local $/; <FIL> };
close FIL;

my @chars = split //, $filstr;
my (%charhash, $charstot);
map { $charhash{$_}++; $charstot++ } @chars;
my @values = map { $_ / $charstot } values %charhash;
my $ent = entropy(\@values);

printf ("file %s\ncontents     entropy = %20.15f\n",$fil,$ent);


sub entropy{
  my ($listr, $baselog) = @_;
  $baselog = 0.693147180559945 unless $baselog; # log(2)
  return undef unless ref $listr;
  my $sum;
  my @nums = @$listr;
  map { $sum += $_ * (log($_)/$baselog) } @nums;
  return -$sum;  
}