> 	((int)val & 0x100) == 0
> 
> (if 'val' is signed and negative, it'll be sign-extended, so bits
> above the low 8 will be set.  otherwise those bits will be zero.)

If we were willing to require ANSI C,

	(signed char)val >= 0

would express the intent more directly.  (As it stands, you lose on machines
with 10 bit characters (anyone working on a port to the BBN C Machine? ;-))