#!/usr/bin/perl
# entropy.pl - Don Yang (uguu.org)
#
# 02/17/03


while( $#ARGV >= 0 )
{
   $filename = shift @ARGV;
   $filesize = 0;
   @freq = ();
   open INFILE, "< $filename" or die;
   while( defined($i = getc(INFILE)) )
   {
      $freq[ord $i]++;
      $filesize++;
   }
   close INFILE;

   $entropy = 0;
   for($i = 0; $i < 256; $i++)
   {
      if( $freq[$i] )
      {
         $p = $freq[$i] / $filesize;
         $entropy -= $p * log($p) / log(2);
      }
   }
   print "$filename: $entropy bits\n";
}