1------------------------------------------------------------------------------
2--                                                                          --
3--                         GNAT RUN-TIME COMPONENTS                         --
4--                                                                          --
5--                       S Y S T E M . P A C K _ 2 4                        --
6--                                                                          --
7--                                 B o d y                                  --
8--                                                                          --
9--          Copyright (C) 1992-2009, Free Software Foundation, Inc.         --
10--                                                                          --
11-- GNAT is free software;  you can  redistribute it  and/or modify it under --
12-- terms of the  GNU General Public License as published  by the Free Soft- --
13-- ware  Foundation;  either version 3,  or (at your option) any later ver- --
14-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
15-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
16-- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
17--                                                                          --
18-- As a special exception under Section 7 of GPL version 3, you are granted --
19-- additional permissions described in the GCC Runtime Library Exception,   --
20-- version 3.1, as published by the Free Software Foundation.               --
21--                                                                          --
22-- You should have received a copy of the GNU General Public License and    --
23-- a copy of the GCC Runtime Library Exception along with this program;     --
24-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
25-- <http://www.gnu.org/licenses/>.                                          --
26--                                                                          --
27-- GNAT was originally developed  by the GNAT team at  New York University. --
28-- Extensive contributions were provided by Ada Core Technologies Inc.      --
29--                                                                          --
30------------------------------------------------------------------------------
31
32with System.Storage_Elements;
33with System.Unsigned_Types;
34with Ada.Unchecked_Conversion;
35
36package body System.Pack_24 is
37
38   subtype Ofs is System.Storage_Elements.Storage_Offset;
39   subtype Uns is System.Unsigned_Types.Unsigned;
40   subtype N07 is System.Unsigned_Types.Unsigned range 0 .. 7;
41
42   use type System.Storage_Elements.Storage_Offset;
43   use type System.Unsigned_Types.Unsigned;
44
45   type Cluster is record
46      E0, E1, E2, E3, E4, E5, E6, E7 : Bits_24;
47   end record;
48
49   for Cluster use record
50      E0 at 0 range 0 * Bits .. 0 * Bits + Bits - 1;
51      E1 at 0 range 1 * Bits .. 1 * Bits + Bits - 1;
52      E2 at 0 range 2 * Bits .. 2 * Bits + Bits - 1;
53      E3 at 0 range 3 * Bits .. 3 * Bits + Bits - 1;
54      E4 at 0 range 4 * Bits .. 4 * Bits + Bits - 1;
55      E5 at 0 range 5 * Bits .. 5 * Bits + Bits - 1;
56      E6 at 0 range 6 * Bits .. 6 * Bits + Bits - 1;
57      E7 at 0 range 7 * Bits .. 7 * Bits + Bits - 1;
58   end record;
59
60   for Cluster'Size use Bits * 8;
61
62   for Cluster'Alignment use Integer'Min (Standard'Maximum_Alignment,
63     1 +
64     1 * Boolean'Pos (Bits mod 2 = 0) +
65     2 * Boolean'Pos (Bits mod 4 = 0));
66   --  Use maximum possible alignment, given the bit field size, since this
67   --  will result in the most efficient code possible for the field.
68
69   type Cluster_Ref is access Cluster;
70
71   function To_Ref is new
72     Ada.Unchecked_Conversion (System.Address, Cluster_Ref);
73
74   --  The following declarations are for the case where the address
75   --  passed to GetU_24 or SetU_24 is not guaranteed to be aligned.
76   --  These routines are used when the packed array is itself a
77   --  component of a packed record, and therefore may not be aligned.
78
79   type ClusterU is new Cluster;
80   for ClusterU'Alignment use 1;
81
82   type ClusterU_Ref is access ClusterU;
83
84   function To_Ref is new
85     Ada.Unchecked_Conversion (System.Address, ClusterU_Ref);
86
87   ------------
88   -- Get_24 --
89   ------------
90
91   function Get_24 (Arr : System.Address; N : Natural) return Bits_24 is
92      C : constant Cluster_Ref := To_Ref (Arr + Bits * Ofs (Uns (N) / 8));
93   begin
94      case N07 (Uns (N) mod 8) is
95         when 0 => return C.E0;
96         when 1 => return C.E1;
97         when 2 => return C.E2;
98         when 3 => return C.E3;
99         when 4 => return C.E4;
100         when 5 => return C.E5;
101         when 6 => return C.E6;
102         when 7 => return C.E7;
103      end case;
104   end Get_24;
105
106   -------------
107   -- GetU_24 --
108   -------------
109
110   function GetU_24 (Arr : System.Address; N : Natural) return Bits_24 is
111      C : constant ClusterU_Ref := To_Ref (Arr + Bits * Ofs (Uns (N) / 8));
112   begin
113      case N07 (Uns (N) mod 8) is
114         when 0 => return C.E0;
115         when 1 => return C.E1;
116         when 2 => return C.E2;
117         when 3 => return C.E3;
118         when 4 => return C.E4;
119         when 5 => return C.E5;
120         when 6 => return C.E6;
121         when 7 => return C.E7;
122      end case;
123   end GetU_24;
124
125   ------------
126   -- Set_24 --
127   ------------
128
129   procedure Set_24 (Arr : System.Address; N : Natural; E : Bits_24) is
130      C : constant Cluster_Ref := To_Ref (Arr + Bits * Ofs (Uns (N) / 8));
131   begin
132      case N07 (Uns (N) mod 8) is
133         when 0 => C.E0 := E;
134         when 1 => C.E1 := E;
135         when 2 => C.E2 := E;
136         when 3 => C.E3 := E;
137         when 4 => C.E4 := E;
138         when 5 => C.E5 := E;
139         when 6 => C.E6 := E;
140         when 7 => C.E7 := E;
141      end case;
142   end Set_24;
143
144   -------------
145   -- SetU_24 --
146   -------------
147
148   procedure SetU_24 (Arr : System.Address; N : Natural; E : Bits_24) is
149      C : constant ClusterU_Ref := To_Ref (Arr + Bits * Ofs (Uns (N) / 8));
150   begin
151      case N07 (Uns (N) mod 8) is
152         when 0 => C.E0 := E;
153         when 1 => C.E1 := E;
154         when 2 => C.E2 := E;
155         when 3 => C.E3 := E;
156         when 4 => C.E4 := E;
157         when 5 => C.E5 := E;
158         when 6 => C.E6 := E;
159         when 7 => C.E7 := E;
160      end case;
161   end SetU_24;
162
163end System.Pack_24;
164