/* shia1.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;
   FILE *infile;

   if( argc < 2 )
   {
      printf("%s <filename> [...]\n", *argv);
   }
   else
   {
      for(a = 1; a < argc; a++)
      {
         if( (infile = fopen(argv[a], "rb")) )
         {
            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) / log(2);
               }
            printf("%s: %f bits\n", argv[a], entropy);
         }
      }
   }
   return 0;
}