1------------------------------------------------------------------------------
2--                                                                          --
3--                         GNAT COMPILER COMPONENTS                         --
4--                                                                          --
5--                               T T Y P E S                                --
6--                                                                          --
7--                                 S p e c                                  --
8--                                                                          --
9--          Copyright (C) 1992-2013, 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.  See the GNU General Public License --
17-- for  more details.  You should have  received  a copy of the GNU General --
18-- Public License  distributed with GNAT; see file COPYING3.  If not, go to --
19-- http://www.gnu.org/licenses for a complete copy of the license.          --
20--                                                                          --
21-- GNAT was originally developed  by the GNAT team at  New York University. --
22-- Extensive contributions were provided by Ada Core Technologies Inc.      --
23--                                                                          --
24------------------------------------------------------------------------------
25
26--  This package contains constants describing target properties
27
28with Types;    use Types;
29with Get_Targ;
30with Set_Targ;
31
32package Ttypes is
33
34   ------------------------------
35   -- Host/Target Dependencies --
36   ------------------------------
37
38   --  It is vital to maintain a clear distinction between properties of
39   --  types on the host and types on the target, since in the general
40   --  case of a cross-compiler these will be different.
41
42   --  This package provides definitions of values that describe the properties
43   --  of the target types. All instances of target dependencies, including the
44   --  definitions of such packages as Standard and System depend directly or
45   --  indirectly on the definitions in the Ttypes packages.
46
47   --  In the source of the compiler, references to attributes such as
48   --  Integer'Size will give information regarding the host types (i.e.
49   --  the types within the compiler itself). Such references are therefore
50   --  almost always suspicious (it is hard for example to see that the
51   --  code in the compiler should even be using type Integer very much,
52   --  and certainly this code should not depend on the size of Integer).
53
54   --  On the other hand, it is perfectly reasonable for the compiler to
55   --  require access to the size of type Integer for the target machine,
56   --  e.g. in constructing the internal representation of package Standard.
57   --  For this purpose, instead of referencing the attribute Integer'Size,
58   --  a reference to Ttypes.Standard_Integer_Size will provide the needed
59   --  value for the target type.
60
61   --  Two approaches are used for handling target dependent values in the
62   --  standard library packages. Package Standard is handled specially,
63   --  being constructed internally (by package Stand). Target dependent
64   --  values needed in Stand are obtained by direct reference to Ttypes
65   --  and Ttypef.
66
67   --  For package System, the required constant values are obtained by
68   --  referencing appropriate attributes. Ada 95 already defines most of
69   --  the required attributes, and GNAT specific attributes have been
70   --  defined to cover the remaining cases (such as Storage_Unit). The
71   --  evaluation of these attributes obtains the required target dependent
72   --  values from Ttypes and Ttypef. The additional attributes that have
73   --  been added to GNAT (Address_Size, Storage_Unit, Word_Size, Max_Priority,
74   --  and Max_Interrupt_Priority) are for almost all purposes redundant with
75   --  respect to the corresponding references to System constants. For example
76   --  in a program, System.Address_Size and Standard'Address_Size yield the
77   --  same value. The critical use of the attribute is in writing the System
78   --  declaration of Address_Size which of course cannot refer to itself. By
79   --  this means we achieve complete target independence in the source code
80   --  of package System, i.e. there is only one copy of the source of System
81   --  for all targets.
82
83   --  Note that during compilation there are two versions of package System
84   --  around. The version that is directly with'ed by compiler packages
85   --  contains host-dependent definitions, which is what is needed in that
86   --  case (for example, System.Storage_Unit referenced in the source of the
87   --  compiler refers to the storage unit of the host, not the target). This
88   --  means that, like attribute references, any references to constants in
89   --  package System in the compiler code are suspicious, since it is strange
90   --  for the compiler to have such host dependencies. If the compiler needs
91   --  to access the target dependent values of such quantities as Storage_Unit
92   --  then it should reference the constants in this package (Ttypes), rather
93   --  than referencing System.Storage_Unit, or Standard'Storage_Unit, both of
94   --  which would yield the host value.
95
96   ---------------------------------------------------
97   -- Target-Dependent Values for Types in Standard --
98   ---------------------------------------------------
99
100   --  Note: GNAT always supplies all the following integer and float types,
101   --  but depending on the machine, some of the types may be identical. For
102   --  example, on some machines, Short_Float may be the same as Float, and
103   --  Long_Long_Float may be the same as Long_Float.
104
105   Standard_Short_Short_Integer_Size  : constant Pos :=
106                                          Set_Targ.Char_Size;
107   Standard_Short_Short_Integer_Width : constant Pos :=
108                                          Get_Targ.Width_From_Size
109                                           (Standard_Short_Short_Integer_Size);
110
111   Standard_Short_Integer_Size        : constant Pos :=
112                                          Set_Targ.Short_Size;
113   Standard_Short_Integer_Width       : constant Pos :=
114                                          Get_Targ.Width_From_Size
115                                            (Standard_Short_Integer_Size);
116
117   Standard_Integer_Size              : constant Pos :=
118                                          Set_Targ.Int_Size;
119   Standard_Integer_Width             : constant Pos :=
120                                          Get_Targ.Width_From_Size
121                                            (Standard_Integer_Size);
122
123   Standard_Long_Integer_Size         : constant Pos :=
124                                          Set_Targ.Long_Size;
125   Standard_Long_Integer_Width        : constant Pos :=
126                                          Get_Targ.Width_From_Size
127                                            (Standard_Long_Integer_Size);
128
129   Standard_Long_Long_Integer_Size    : constant Pos :=
130                                          Set_Targ.Long_Long_Size;
131   Standard_Long_Long_Integer_Width   : constant Pos :=
132                                          Get_Targ.Width_From_Size
133                                            (Standard_Long_Long_Integer_Size);
134
135   Standard_Short_Float_Size          : constant Pos :=
136                                          Set_Targ.Float_Size;
137   Standard_Short_Float_Digits        : constant Pos :=
138                                          Get_Targ.Digits_From_Size
139                                            (Standard_Short_Float_Size);
140
141   Standard_Float_Size                : constant Pos :=
142                                          Set_Targ.Float_Size;
143   Standard_Float_Digits              : constant Pos :=
144                                          Get_Targ.Digits_From_Size
145                                            (Standard_Float_Size);
146
147   Standard_Long_Float_Size           : constant Pos :=
148                                          Set_Targ.Double_Size;
149   Standard_Long_Float_Digits         : constant Pos :=
150                                          Get_Targ.Digits_From_Size
151                                            (Standard_Long_Float_Size);
152
153   Standard_Long_Long_Float_Size      : constant Pos :=
154                                          Set_Targ.Long_Double_Size;
155   Standard_Long_Long_Float_Digits    : constant Pos :=
156                                          Get_Targ.Digits_From_Size
157                                            (Standard_Long_Long_Float_Size);
158
159   Standard_Character_Size            : constant Pos := Set_Targ.Char_Size;
160
161   Standard_Wide_Character_Size       : constant Pos := 16;
162   Standard_Wide_Wide_Character_Size  : constant Pos := 32;
163   --  Standard wide character sizes
164
165   --  Note: there is no specific control over the representation of
166   --  enumeration types. The convention used is that if an enumeration
167   --  type has fewer than 2**(Character'Size) elements, then the size
168   --  used is Character'Size, otherwise Integer'Size is used.
169
170   --  Similarly, the size of fixed-point types depends on the size of the
171   --  corresponding integer type, which is the smallest predefined integer
172   --  type capable of representing the required range of values.
173
174   -------------------------------------------------
175   -- Target-Dependent Values for Types in System --
176   -------------------------------------------------
177
178   System_Address_Size : constant Pos := Set_Targ.Pointer_Size;
179   --  System.Address'Size (also size of all thin pointers)
180
181   System_Max_Binary_Modulus_Power : constant Pos :=
182                                       Standard_Long_Long_Integer_Size;
183
184   System_Max_Nonbinary_Modulus_Power : constant Pos := Standard_Integer_Size;
185
186   System_Storage_Unit : constant Pos := Set_Targ.Bits_Per_Unit;
187   System_Word_Size    : constant Pos := Set_Targ.Bits_Per_Word;
188
189   System_Tick_Nanoseconds : constant Pos := 1_000_000_000;
190   --  Value of System.Tick in nanoseconds. At the moment, this is a fixed
191   --  constant (with value of 1.0 seconds), but later we should add this
192   --  value to the GCC configuration file so that its value can be made
193   --  configuration dependent.
194
195   -----------------------------------------------------
196   -- Target-Dependent Values for Types in Interfaces --
197   -----------------------------------------------------
198
199   Interfaces_Wchar_T_Size : constant Pos := Set_Targ.Wchar_T_Size;
200
201   ----------------------------------------
202   -- Other Target-Dependent Definitions --
203   ----------------------------------------
204
205   Maximum_Alignment : constant Pos := Set_Targ.Maximum_Alignment;
206   --  The maximum alignment, in storage units, that an object or type may
207   --  require on the target machine.
208
209   System_Allocator_Alignment : constant Pos :=
210                                  Set_Targ.System_Allocator_Alignment;
211   --  The alignment in storage units of addresses returned by malloc
212
213   Max_Unaligned_Field : constant Pos := Set_Targ.Max_Unaligned_Field;
214   --  The maximum supported size in bits for a field that is not aligned
215   --  on a storage unit boundary.
216
217   Bytes_Big_Endian : Boolean := Set_Targ.Bytes_BE /= 0;
218   --  Important note: for Ada purposes, the important setting is the bytes
219   --  endianness (Bytes_Big_Endian), not the bits value (Bits_Big_Endian).
220   --  This is because Ada bit addressing must be compatible with the byte
221   --  ordering (otherwise we would end up with non-contiguous fields). It
222   --  is rare for the two to be different, but if they are, Bits_Big_Endian
223   --  is relevant only for the generation of instructions with bit numbers,
224   --  and thus relevant only to the back end. Note that this is a variable
225   --  rather than a constant, since it can be modified (flipped) by -gnatd8.
226
227   Target_Short_Enums : constant Boolean := Set_Targ.Short_Enums /= 0;
228   --  True if we are in short enums mode, where foreign convention
229   --  (in particular C and C++) enumeration types will be sized as in Ada,
230   --  using the shortest possibility from 8,16,32 bits, signed or unsigned.
231   --  A zero value means Short_Enums are not in use, and in this case all
232   --  foreign convention enumeration types are given the same size as c int.
233
234   Target_Strict_Alignment : Boolean :=
235                               Set_Targ.Strict_Alignment /= 0;
236   --  True if instructions will fail if data is misaligned. Note that this
237   --  is a variable rather than a constant since it can be modified (set to
238   --  True) if the debug flag -gnatd.A is used.
239
240   Target_Double_Float_Alignment : constant Nat :=
241                                     Set_Targ.Double_Float_Alignment;
242   --  The default alignment of "double" floating-point types, i.e. floating
243   --  point types whose size is equal to 64 bits, or 0 if this alignment is
244   --  not lower than the largest power of 2 multiple of System.Storage_Unit
245   --  that does not exceed either the object size of the type or the maximum
246   --  allowed alignment.
247
248   Target_Double_Scalar_Alignment : constant Nat :=
249                                      Set_Targ.Double_Scalar_Alignment;
250   --  The default alignment of "double" or larger scalar types, i.e. scalar
251   --  types whose size is greater or equal to 64 bits, or 0 if this alignment
252   --  is not lower than the largest power of 2 multiple of System.Storage_Unit
253   --  that does not exceed either the object size of the type or the maximum
254   --  allowed alignment.
255
256end Ttypes;
257