draft ANSI standard: one change that would *really* help Europe

[Kenneth R. Ballou]

In article <518 at brl-sem.ARPA> ron at brl-sem.ARPA (Ron Natalie <ron>) writes:
> ... nowhere is it stated that (unsigned) -1 will give you a word of
>all ones.  Becareful when making this assumption.  I spend a lot of time
>fixing up the Berkeley network code because of this.

	Actually, I think (unsigned) -1 does have to give you a bit pattern of
all 1's.  I can not find an explicit reason, but I can deduce this from the
following:

	1.  Harbison and Steele, page 89:
	    "No matter what representation is used for signed integers,
	an unsigned integer represented with n bits is always considered to
	be in straight unsigned binary notation, with values ranging from
	0 through 2^n-1.  Therefore, the bit pattern for a given unsigned
	value is predictable and portable, whereas the bit pattern for a
	given signed value is not predictable and not portable."

	2.  Harbison and Steele, pages 126-7 (talking about casting an integral
	    type into an unsigned integral type):
	    "  If the result type is an unsigned type, then the result
	must be that unique alue of the result type that is equal (congruent)
	mod 2^n in the original value, where n is equal to the number of bits
	used in the representation of the result type."

	3.  The value in the range 0 to 2^n-1 (inclusive) congruent mod 2^n
	to -1 is 2^n-1.  In straight binary notation this value is repre-
	sented as all 1's.

--------
Kenneth R. Ballou			ARPA:  ballou at brahms
Department of Mathematics		UUCP:  ...!ucbvax!brahms!ballou
University of California
Berkeley, California  94720
--------
Kenneth R. Ballou			ARPA:  ballou at brahms
Department of Mathematics		UUCP:  ...!ucbvax!brahms!ballou
University of California
Berkeley, California  94720