1------------------------------------------------------------------------------
2--                                                                          --
3--                         GNAT COMPILER COMPONENTS                         --
4--                                                                          --
5--                               T T Y P E S                                --
6--                                                                          --
7--                                 S p e c                                  --
8--                                                                          --
9--          Copyright (C) 1992-2020, 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 Set_Targ;
30
31package Ttypes is
32
33   ------------------------------
34   -- Host/Target Dependencies --
35   ------------------------------
36
37   --  It is vital to maintain a clear distinction between properties of
38   --  types on the host and types on the target, since in the general
39   --  case of a cross-compiler these will be different.
40
41   --  This package provides definitions of values that describe the properties
42   --  of the target types. All instances of target dependencies, including the
43   --  definitions of such packages as Standard and System depend directly or
44   --  indirectly on the definitions in the Ttypes packages.
45
46   --  In the source of the compiler, references to attributes such as
47   --  Integer'Size will give information regarding the host types (i.e.
48   --  the types within the compiler itself). Such references are therefore
49   --  almost always suspicious (it is hard for example to see that the
50   --  code in the compiler should even be using type Integer very much,
51   --  and certainly this code should not depend on the size of Integer).
52
53   --  On the other hand, it is perfectly reasonable for the compiler to
54   --  require access to the size of type Integer for the target machine,
55   --  e.g. in constructing the internal representation of package Standard.
56   --  For this purpose, instead of referencing the attribute Integer'Size,
57   --  a reference to Ttypes.Standard_Integer_Size will provide the needed
58   --  value for the target type.
59
60   --  Two approaches are used for handling target dependent values in the
61   --  standard library packages. Package Standard is handled specially,
62   --  being constructed internally (by package Stand). Target dependent
63   --  values needed in Stand are obtained by direct reference to Ttypes
64   --  and Ttypef.
65
66   --  For package System, there is a separate version for each target, with
67   --  explicit declarations of the required, constants.
68
69   --  Historical note: Originally we had in mind dealing with target dependent
70   --  differences by referencing appropriate attributes. Ada 95 already
71   --  defines most of the required attributes, and GNAT specific attributes
72   --  were defined to cover the remaining cases (such as Storage_Unit).
73   --  The additional attributes that have been added to GNAT (Address_Size,
74   --  Storage_Unit, and Word_Size) are redundant with respect to the
75   --  corresponding references to System constants. For example in a program,
76   --  System.Address_Size and Standard'Address_Size yield the same value.
77   --  These attributes have been retained for compatibility purposes, but
78   --  serve no purpose at this stage.
79
80   --  Note that during compilation there are two versions of package System
81   --  around. The version that is directly with'ed by compiler packages
82   --  contains host-dependent definitions, which is what is needed in that
83   --  case (for example, System.Storage_Unit referenced in the source of the
84   --  compiler refers to the storage unit of the host, not the target). This
85   --  means that, like attribute references, any references to constants in
86   --  package System in the compiler code are suspicious, since it is strange
87   --  for the compiler to have such host dependencies. If the compiler needs
88   --  to access the target dependent values of such quantities as Storage_Unit
89   --  then it should reference the constants in this package (Ttypes), rather
90   --  than referencing System.Storage_Unit, or Standard'Storage_Unit, both of
91   --  which would yield the host value.
92
93   ---------------------------------------------------
94   -- Target-Dependent Values for Types in Standard --
95   ---------------------------------------------------
96
97   --  Note: GNAT always supplies all the following integer and float types,
98   --  but depending on the machine, some of the types may be identical. For
99   --  example, on some machines, Short_Float may be the same as Float, and
100   --  Long_Long_Float may be the same as Long_Float.
101
102   Standard_Short_Short_Integer_Size  : constant Pos :=
103                                          Set_Targ.Char_Size;
104
105   Standard_Short_Integer_Size        : constant Pos :=
106                                          Set_Targ.Short_Size;
107
108   Standard_Integer_Size              : constant Pos :=
109                                          Set_Targ.Int_Size;
110
111   Standard_Long_Integer_Size         : constant Pos :=
112                                          Set_Targ.Long_Size;
113
114   Standard_Long_Long_Integer_Size    : constant Pos :=
115                                          Set_Targ.Long_Long_Size;
116
117   Standard_Long_Long_Long_Integer_Size : Pos :=
118                                            Set_Targ.Long_Long_Long_Size;
119
120   Standard_Short_Float_Size          : constant Pos :=
121                                          Set_Targ.Float_Size;
122
123   Standard_Float_Size                : constant Pos :=
124                                          Set_Targ.Float_Size;
125
126   Standard_Long_Float_Size           : constant Pos :=
127                                          Set_Targ.Double_Size;
128
129   Standard_Long_Long_Float_Size      : constant Pos :=
130                                          Set_Targ.Long_Double_Size;
131
132   Standard_Character_Size            : constant Pos := Set_Targ.Char_Size;
133
134   Standard_Wide_Character_Size       : constant Pos := 16;
135   Standard_Wide_Wide_Character_Size  : constant Pos := 32;
136   --  Standard wide character sizes
137
138   --  Note: there is no specific control over the representation of
139   --  enumeration types. The convention used is that if an enumeration
140   --  type has fewer than 2**(Character'Size) elements, then the size
141   --  used is Character'Size, otherwise Integer'Size is used.
142
143   --  Similarly, the size of fixed-point types depends on the size of the
144   --  corresponding integer type, which is the smallest predefined integer
145   --  type capable of representing the required range of values.
146
147   -------------------------------------------------
148   -- Target-Dependent Values for Types in System --
149   -------------------------------------------------
150
151   System_Address_Size : constant Pos := Set_Targ.Pointer_Size;
152   --  System.Address'Size (also size of all thin pointers)
153
154   System_Max_Integer_Size : Pos := Standard_Long_Long_Long_Integer_Size;
155
156   System_Max_Binary_Modulus_Power : Pos :=
157                                       Standard_Long_Long_Long_Integer_Size;
158
159   System_Max_Nonbinary_Modulus_Power : constant Pos := Standard_Integer_Size;
160
161   System_Storage_Unit : constant Pos := Set_Targ.Bits_Per_Unit;
162   System_Word_Size    : constant Pos := Set_Targ.Bits_Per_Word;
163
164   System_Tick_Nanoseconds : constant Pos := 1_000_000_000;
165   --  Value of System.Tick in nanoseconds. At the moment, this is a fixed
166   --  constant (with value of 1.0 seconds), but later we should add this
167   --  value to the GCC configuration file so that its value can be made
168   --  configuration dependent.
169
170   -----------------------------------------------------
171   -- Target-Dependent Values for Types in Interfaces --
172   -----------------------------------------------------
173
174   Interfaces_Wchar_T_Size : constant Pos := Set_Targ.Wchar_T_Size;
175
176   ----------------------------------------
177   -- Other Target-Dependent Definitions --
178   ----------------------------------------
179
180   Maximum_Alignment : constant Pos := Set_Targ.Maximum_Alignment;
181   --  The maximum alignment, in storage units, that an object or type may
182   --  require on the target machine.
183
184   System_Allocator_Alignment : constant Pos :=
185                                  Set_Targ.System_Allocator_Alignment;
186   --  The alignment in storage units of addresses returned by malloc
187
188   Max_Unaligned_Field : constant Pos := Set_Targ.Max_Unaligned_Field;
189   --  The maximum supported size in bits for a field that is not aligned
190   --  on a storage unit boundary.
191
192   Bytes_Big_Endian : Boolean := Set_Targ.Bytes_BE /= 0;
193   --  Important note: for Ada purposes, the important setting is the bytes
194   --  endianness (Bytes_Big_Endian), not the bits value (Bits_Big_Endian).
195   --  This is because Ada bit addressing must be compatible with the byte
196   --  ordering (otherwise we would end up with non-contiguous fields). It
197   --  is rare for the two to be different, but if they are, Bits_Big_Endian
198   --  is relevant only for the generation of instructions with bit numbers,
199   --  and thus relevant only to the back end. Note that this is a variable
200   --  rather than a constant, since it can be modified (flipped) by -gnatd8.
201
202   Target_Short_Enums : constant Boolean := Set_Targ.Short_Enums /= 0;
203   --  True if we are in short enums mode, where foreign convention
204   --  (in particular C and C++) enumeration types will be sized as in Ada,
205   --  using the shortest possibility from 8,16,32 bits, signed or unsigned.
206   --  A zero value means Short_Enums are not in use, and in this case all
207   --  foreign convention enumeration types are given the same size as c int.
208
209   Target_Strict_Alignment : Boolean :=
210                               Set_Targ.Strict_Alignment /= 0;
211   --  True if instructions will fail if data is misaligned. Note that this
212   --  is a variable rather than a constant since it can be modified (set to
213   --  True) if the debug flag -gnatd.A is used.
214
215   Target_Double_Float_Alignment : constant Nat :=
216                                     Set_Targ.Double_Float_Alignment;
217   --  The default alignment of "double" floating-point types, i.e. floating
218   --  point types whose size is equal to 64 bits, or 0 if this alignment is
219   --  not lower than the largest power of 2 multiple of System.Storage_Unit
220   --  that does not exceed either the object size of the type or the maximum
221   --  allowed alignment.
222
223   Target_Double_Scalar_Alignment : constant Nat :=
224                                      Set_Targ.Double_Scalar_Alignment;
225   --  The default alignment of "double" or larger scalar types, i.e. scalar
226   --  types whose size is greater or equal to 64 bits, or 0 if this alignment
227   --  is not lower than the largest power of 2 multiple of System.Storage_Unit
228   --  that does not exceed either the object size of the type or the maximum
229   --  allowed alignment.
230
231end Ttypes;
232