void dump_hex (void *ptr, int buflen)
{
   unsigned char *buf = (unsigned char*)ptr;
   int i, j;
   for (i=0; i < buflen; i+=16)
   {
      printf("%08X: ", buf);
      for (j=0; j < 16; j++)
         if (i+j < buflen)
            printf("%02X ", buf[i+j]);
         else
            printf("   ");
      printf(" ");
      for (j=0; j < 16; j++)
         if (i+j < buflen)
            printf("%c", buf[i+j] >= 0x20 && buf[i+j] < 0x7f ? buf[i+j] : '.');
      printf("\n");
   }
}