VHDL Issue Number:      0188
Classification:         Language Definition Problem
Language Version:       VHDL-87
Summary:                VPI Issue 12 -- Range direction in qual. exps.
Related Issues:         TBD
Relevant LRM Sections:  TBD
Key Words and Phrases:  TBD
Current Status:         Superseded
1076-1993 Disposition:  Superseded (ISAC Issues Outstanding)
Disposition Rationale:  none.
Superseded By:          0050 (Previously)
-----------------------
Date Submitted:         1991/03/15
Author of Submission:   J. R. Armstrong
Author's Affiliation:   Virginia Polytechnic Institute and State University
Author's Post Address:  Bradley Department of Electrical Engineering
                        Virginia Polytechnic Institute and State University
                        Blacksburg, VA 24061
Author's Phone Number:  (703) 231-4723
Author's Fax Number:    
Author's Net Address:   JRA@VTVM1.CC.VT.EDU
-----------------------
Date Analyzed:          1992/01/02
Author of Analysis:     Alex Zamfirescu 
Revision Number:        $Revision: 1.9 $
Date Last Revised:      $Date: 1995/05/13 21:53:48 $


Description of Problem
----------------------
  Can a range within a qualified expression be spec-
  ified  as  an  ascending range when it was declared as a de-
  scending range?

  Test File: ch07/s03/s2/s2/04020101.vhd


 
--##73224211245FF*************************************************************
 --
  --+ File: [SUITE.CH07.S03.S2.S2]04020101.VHD
  --
  --+ Copyright: (c) 1986 by Intermetrics Inc. All rights reserved
  --
  --+ LRM_Version: IEEE Std. 1076-1987
  --
  --+ Subsets: None
  --
  --+ Description:
  --
  --+ Test_point -      (070322_040201)  "For  an  array aggregate that does
not
  --                    have an others choice, if the aggregate appears
  --                    in  one  of  the  contexts  described in the test
points
  --                    070322_030201 through 070322_031001,  the  direction 
of
  --                    the  index subtype of the aggregate is that of the
  --                    corresponding constrained array subtype."
  --
  --
  --+ Test_objective (1) - Test that the direction of the index subtype of the
  --                  aggregate array is the same as the direction of the index
  --                  subtype of the base type of the array.
  --
  --+ References: None
  --
  --+ Instructions: None
  --
  --+ Keywords:  Array aggregate, index subtype
  --
  --+ Test_Results: Expect_Success. Output_Checked.
  --
  --+ Test_Type: Locally Static Semantic
  --
  --+ History: Created MM/MCC 7-13-89
  --           Modified CHC/VT 8-29-89
  --           Corrected KSC/VT 12-22-89
  --           Modified CHC/VT  5-4-90
  --
  --+ Comments:  Original file name: E-07-2-2-2211A.VHD
  --             Updated package declaration  Sun Oct  2 14:55:11 1988
  --                                              (David)Franke@mcc.com
  --             Updated to 1076-1987 VHDL, checked w/Recognizer.
  --                                          (Steve)Grout@mcc.com 20jun88
  --
  --             Zycad claimed that this should be an expect failure test
  --             because of the direction of the range of CA_DOWN in
  --             the return statement.
  --             This will be sent to VASG for clarification.
 
--****************************************************************************
  package P1 is

       type UNCONSTRAINED_ARRAY is array ( integer range <> ) of character;

          subtype CA_UP is UNCONSTRAINED_ARRAY ( 1 to 10 );
          subtype CA_DOWN is UNCONSTRAINED_ARRAY (10 downto 1);

       function F_bad (C : CA_UP) return CA_UP;

  end P1;

  package body  P1 is
  function F_bad (C : CA_UP) return CA_UP is
      begin
        return CA_DOWN'((1 to 10 => 'B')); -- No_failure_here
  end F_bad;

  end P1;

  use work.P1.all;
  entity E is
  end E;


Proposed Resolution
-------------------
The direction of a discrete range is used in an aggregate just to
express a correct discrete range, and it has no other significance.


VASG-ISAC Analysis & Rationale
------------------------------  
VASG-ISAC Recommendation for IEEE Std 1076-1987 for the ISAC-Approved
VHDL Issue Number 0050 solves the problem raised by this IR. 

       The intent of the language is to allow any direction
       of a discrete range that appears in an aggregate. 
       The direction of a discrete range is used in an 
       aggregate just to express a correct discrete range,
       and it has no other significance.

Test is correct VHDL code, excepting the subtype of the return value
in function F_bad that has to be CA_UP.


VASG-ISAC Recommendation for IEEE Std 1076-1987
-----------------------------------------------
Refer to IR-0050. The present IR is now superseded by IR-0050. 


VASG-ISAC Recommendation for Future Revisions
---------------------------------------------
See issue Report 0050.