!standard A.5.3    (50)                               99-07-08  AI95-00055/02
!class confirmation 95-06-25
!status WG9 Approved  97-11-14
!status ARG approved (6-1-0) subject to editorial review 97-04-11
!status work item 95-06-25
!status received 95-06-25
!priority Low
!difficulty Easy
!subject Overflow for Adjacent, Machine, and Model attributes

!summary

The Adjacent, Machine, and Model attributes raise Constraint_Error under
the conditions specified in the RM, even if the Machine_Overflows
attribute is False.

!question

The Adjacent, Machine, and Model attributes raise Constraint_Error under
certain overflow conditions (see A.5.3(50,62), G.2.2(07)).  The
description does not mention Machine_Overflows.  Thus, Constraint_Error
is raised even if Machine_Overflows is False.  Is this the intent?
(Yes.)

!response

The intent is that Machine_Overflows does not affect the raising of
Constraint_Error by the Adjacent, Machine, and Model attributes.
The RM wording is correct as is.

As shown in the AARM, these checks are Range_Checks, not Overflow_Checks.

Furthermore, the efficiency concerns that lead to allowing
Machine_Overflows to be False do not apply here.  These attributes
typically take many machine instructions to execute, as compared to, for
example, a multiply, where an overflow check would be a substantial
relative overhead on some machines.

!ACATS test

It is not possible to test if the Adjacent, Machine, and Model attributes
raise Constraint_Error. Constructing values that would leave the base range
of a type (and trigger the constraint error) would require more knowledge
about the numeric models of an implementation than is available to an ACATS
test.

!appendix

!section A.5.3(50)
!subject Mistake in description for floating point attribute S'Adjacent
!reference RM95-A.5.3(50)
!from Samuel Figueroa (figueroa@cs.nyu.edu) 95-06-16
!reference as: 95-5159.a Samuel Figueroa  95-6-16>>
!discussion

If the result would be outside the base range of S {and S'Machine_Overflows is
True}, Constraint_Error is raised.

****************************************************************

!section A.5.3(62)
!subject Mistake in description for floating point attribute S'Machine
!reference RM95-A.5.3(62)
!from Samuel Figueroa (figueroa@cs.nyu.edu) 95-06-16
!reference as: 95-5159.b Samuel Figueroa  95-6-16>>
!discussion

Constraint_Error is raised if {S'Machine_Overflows is True and} rounding or
truncating X to the precision of the machine numbers results in a value
outside the base range of S.

****************************************************************

!section G.2.2(07)
!subject Mistake in description for floating point attribute S'Model
!reference RM95-G.2.2(7)
!from Samuel Figueroa (figueroa@cs.nyu.edu) 95-06-16
!reference as: 95-5159.c Samuel Figueroa  95-6-16>>
!discussion

Constraint_Error is raised if {S'Machine_Overflows is True and} the resulting
model number is outside the safe range of S.

****************************************************************