#define _LARGEFILE64_SOURCE 1

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>


static FILE *
open_file (const char *filename)
{
  FILE *retval;

  if (strcmp (filename, "-") == 0)
    return stdin;
  
  retval = fopen (filename, "r");
  if (retval == NULL)
    {
      fprintf (stderr, "Error opening \"%s\": %m\n", filename);
      exit (2);
    }

  return retval;
}

static void
close_file (FILE *f, const char *filename)
{
  if (f == stdin)
    return;

  if (fclose (f) != 0)
    {
      fprintf (stderr, "Error closing \"%s\": %m\n", filename);
      exit(2);
    }
}

static int
get_character (FILE *f, const char *filename)
{
  int retval;

  retval = fgetc (f);
  if (ferror (f))
    {
      fprintf (stderr, "Error reading \"%s\": %m\n", filename);
      exit(2);
    }

  return retval;
}

static void
dump_character (int c)
{
/*_(0xXX YYY 'C') */
/*_EOF            */

  if (c == EOF)
    fputs (" EOF            ", stdout);
  else
    {
      printf (" (0x%02x %3d ", c, c);
      if (isprint (c))
        printf ("'%c'", c);
      else
        fputs ("   ", stdout);
      putchar (')');
    }
}

int
main (int argc, char **argv)
{
  int exit_code = 0;
  int argi;

  if (argc < 3)
    {
      fputs ("Syntax: cmpx <file1> <file2> [<file3>...]\n", stderr);
      exit (2);
    }

  for (argi = 1; argi <= argc - 2; argi++)
    {
      FILE *f1, *f2;
      int c1, c2;
      off_t offset;
      char *f1_filename, *f2_filename;
      int need_header = argc > 3;

      f1_filename = argv[argi + 0];
      f2_filename = argv[argi + 1];

      f1 = open_file (f1_filename);
      f2 = open_file (f2_filename);

      for (offset = 0 ;; offset++)
	{
	  c1 = get_character (f1, f1_filename);
	  c2 = get_character (f2, f2_filename);

	  if (c1 == EOF && c2 == EOF)
	    break;
	  if (c1 == c2)
	    continue;

	  if (need_header)
	    {
	      printf ("%s\t%s\n", f1_filename, f2_filename);
	      need_header = 0;
	    }
	  printf ("0x%08llx", (unsigned long long) offset);
	  dump_character (c1);
	  dump_character (c2);
	  putchar ('\n');
	  exit_code = 1;
	}

      close_file (f1, f1_filename);
      close_file (f2, f2_filename);
    }

  return exit_code;
}