tv@pobox.com said:
> - for the best-case workaround, cast these to `int' before checking if
> they
>   are less than 0 (...do not cast to `signed char'). 


This won't help.  

f.c:

main()
{
  char a = 0xf0;

  printf("%d\n", (int) a);
}

$ gcc -funsigned-char f.c
$ ./a.out
240

You need to cast the char to signed before you can then sign-extend it to 
an int.