J3/04-263
                                                                                            J3/04-263
Date 2004-02-29
To:  J3
From: Michael Ingrassia
Subject: Unsigned Integers

The following rules are implemented in shipping compilers.
I propose Unsigned Integers be added to standard Fortran.


o UNSIGNED is an integer type

o an unsigned integer constant is a digit-string followed by the letter U
	or the letter u , optionally followed by an underscore followed by
	a kind parameter; the kind parameters shall match the integer
	kind parameters

o  arithmetic expressions shall not have both signed and unsigned integer
	operands unless
	1) the signed operand has value 0 ; the result type is the unsigned
		integer type
	2) the operation is intrinsic exponentiation; the result type
		is the type of the left operand

o relational expressions shall deliver a result which depends on the
	unaltered values of the operands

	For example:
		Consider a processor in which the kind numbers represent
		   the number of bytes.

		-1_4 .LT. 17U_8    has the value .TRUE.

		since -1 is less than 17.  -1_4 is not widened to -1_8
		and then interpreted as a very large unsigned number.


o the CASE construct shall admit unsigned integer expressions as case-exprs

o (formatted I/O)
	unsigned integers may be read and written using I, B, O, and Z edit
	descriptors
o (namelist I/O)
	unsigned integers may be read and written.  The written form of
	an unsigned integer is the same as the form used for a positive
	unsigned integer.
o (list-directed I/O)
	unsigned integers may be read and written.  Same written form as
	for namelist I/O.
o (unformatted I/O)
	unsigned integers may be read and written.
o Intrinsics
	A new intrinsic function UNSIGNED(A [, KIND]) shall be added,
	analogous to INT, but shall produce a result of unsigned type
	instead of integer type.

	A new intrinsic function SELECTED_UNSIGNED_KIND shall be added.

	Where reasonable, operands which accept an argument of signed
	integer type shall accept an argument of unsigned integer type
	in its place.  But ABS and SIGN shall not accept an argument of
	 unsigned integer type.

	The MAX and MIN intrinsics shall not allow operands of both
	signed and unsigned integer type.

o Assignment shall be value-preserving where possible.

	For example:  Consider a processor in which kind numbers
             represent the number of bytes.
	The assignment
		UNSIGNED(8) U
		SIGNED(4) I
		I = 17_4
		U = I
	gives U the same value represented by literal 17U_8.
	The assignment
		UNSIGNED(1) U
		SIGNED(4) I
		U = 255U_1
                                I = U
      gives I the same value represented by literal 255_8.