/* shia0.c - Don Yang (uguu.org)

   02/17/03
                                                                           */

#include<stdio.h>
#include<math.h>

#define BUFSIZE      8192


int main(int argc, char **argv)
{
   unsigned char buffer[BUFSIZE];
   int a, i, size, filesize, freq[256];
   double p, entropy, log2;
   FILE *infile;

   if( argc < 2 )
      return printf("%s <filename> [...]\n", *argv);

   log2 = log(2);
   for(a = 1; a < argc; a++)
   {
      printf("%s: ", argv[a]);
      if( (infile = fopen(argv[a], "rb")) == NULL )
      {
         puts("fopen() failed");
      }
      else
      {
         for(i = filesize = 0; i < 256; freq[i++] = 0);
         for(; !feof(infile); filesize += size)
         {
            if( !(size = fread(buffer, 1, BUFSIZE, infile)) )
               break;
            for(i = 0; i < size; freq[buffer[i++]]++);
         }
         fclose(infile);
         for(entropy = i = 0; i < 256; i++)
            if( freq[i] )
            {
               p = freq[i] / (double)filesize;
               entropy -= p * log(p) / log2;
            }
         printf("%f bits\n", entropy);
      }
   }

   return 0;
}