[Ada] Proper handling of packed array of small record with reverse SSO

[Arnaud Charlet <charlet at adacore dot com>]

This change ensures proper processing for a packed array of 4-bit records
specified with reverse scalar storage order.

The following program must compile quietly and execute as shown:

$ gnatmake -q reduced_pkd_array_small_rec
$ ./reduced_pkd_array_small_rec
Config 0 =  1
Config 1 =  3
Config 2 =  5
Config 3 =  7
Bit pattern:  19  87

with Ada.Text_Io; use Ada.Text_IO;
with System.Storage_Elements; use System.Storage_Elements;

procedure reduced_pkd_array_small_rec is

    type Int3 is range 0 .. 7;
    for Int3'Size use 3;

    type Small_Rec is record
       B : Boolean := False;
       I : Int3    := 0;
    end record;

    pragma pack (Small_Rec);

    for Small_Rec'Size use 4;
    for Small_Rec'Bit_Order use System.High_Order_First;
    for Small_Rec'Scalar_Storage_Order use System.High_Order_First;

    for Small_Rec use record
        B at 0 range 0 .. 0;
        I at 0 range 1 .. 3;
    end record;

    type Pakd_Array is array (Integer range 0 .. 3) of Small_Rec;
    pragma pack (Pakd_Array);
    for Pakd_Array'Scalar_Storage_Order use System.High_Order_First;

    Config : Pakd_Array;

    SA : Storage_Array (1 .. Config'Size / 8);
    for SA'Address use Config'Address;
    pragma Import (Ada, SA);

begin
    Config(0).I := 1;
    Config(1).I := 3;
    Config(2).I := 5;
    Config(3).I := 7;

    Put_Line ("Config 0 = " & Config(0).I'Img);
    Put_Line ("Config 1 = " & Config(1).I'Img);
    Put_Line ("Config 2 = " & Config(2).I'Img);
    Put_Line ("Config 3 = " & Config(3).I'Img);

    Put ("Bit pattern:");
    for J in SA'Range loop
       Put (" " & SA (J)'Img);
    end loop;
    New_Line;
end;

Tested on x86_64-pc-linux-gnu, committed on trunk

2014-05-21  Thomas Quinot  <quinot@adacore.com>

	* exp_pakd.adb (Byte_Swap): Handle the case of a sub-byte
	component. No byte swapping occurs, but this procedure also takes
	care of appropriately justifying the argument.

Attachment: difs
Description: Text document