File : ttypes.ads
1 ------------------------------------------------------------------------------
2 -- --
3 -- GNAT COMPILER COMPONENTS --
4 -- --
5 -- T T Y P E S --
6 -- --
7 -- S p e c --
8 -- --
9 -- Copyright (C) 1992-2014, 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
28 with Types; use Types;
29 with Get_Targ;
30 with Set_Targ;
31
32 package 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, there is a separate version for each target, with
68 -- explicit declarations of the required, constants.
69
70 -- Historical note: Originally we had in mind dealing with target dependent
71 -- differences by referencing appropriate attributes. Ada 95 already
72 -- defines most of the required attributes, and GNAT specific attributes
73 -- were defined to cover the remaining cases (such as Storage_Unit).
74 -- The additional attributes that have been added to GNAT (Address_Size,
75 -- Storage_Unit, and Word_Size) are redundant with respect to the
76 -- corresponding references to System constants. For example in a program,
77 -- System.Address_Size and Standard'Address_Size yield the same value.
78 -- These attributes have been retained for compatibility purposes, but
79 -- serve no purpose at this stage.
80
81 -- Note that during compilation there are two versions of package System
82 -- around. The version that is directly with'ed by compiler packages
83 -- contains host-dependent definitions, which is what is needed in that
84 -- case (for example, System.Storage_Unit referenced in the source of the
85 -- compiler refers to the storage unit of the host, not the target). This
86 -- means that, like attribute references, any references to constants in
87 -- package System in the compiler code are suspicious, since it is strange
88 -- for the compiler to have such host dependencies. If the compiler needs
89 -- to access the target dependent values of such quantities as Storage_Unit
90 -- then it should reference the constants in this package (Ttypes), rather
91 -- than referencing System.Storage_Unit, or Standard'Storage_Unit, both of
92 -- which would yield the host value.
93
94 ---------------------------------------------------
95 -- Target-Dependent Values for Types in Standard --
96 ---------------------------------------------------
97
98 -- Note: GNAT always supplies all the following integer and float types,
99 -- but depending on the machine, some of the types may be identical. For
100 -- example, on some machines, Short_Float may be the same as Float, and
101 -- Long_Long_Float may be the same as Long_Float.
102
103 Standard_Short_Short_Integer_Size : constant Pos :=
104 Set_Targ.Char_Size;
105 Standard_Short_Short_Integer_Width : constant Pos :=
106 Get_Targ.Width_From_Size
107 (Standard_Short_Short_Integer_Size);
108
109 Standard_Short_Integer_Size : constant Pos :=
110 Set_Targ.Short_Size;
111 Standard_Short_Integer_Width : constant Pos :=
112 Get_Targ.Width_From_Size
113 (Standard_Short_Integer_Size);
114
115 Standard_Integer_Size : constant Pos :=
116 Set_Targ.Int_Size;
117 Standard_Integer_Width : constant Pos :=
118 Get_Targ.Width_From_Size
119 (Standard_Integer_Size);
120
121 Standard_Long_Integer_Size : constant Pos :=
122 Set_Targ.Long_Size;
123 Standard_Long_Integer_Width : constant Pos :=
124 Get_Targ.Width_From_Size
125 (Standard_Long_Integer_Size);
126
127 Standard_Long_Long_Integer_Size : constant Pos :=
128 Set_Targ.Long_Long_Size;
129 Standard_Long_Long_Integer_Width : constant Pos :=
130 Get_Targ.Width_From_Size
131 (Standard_Long_Long_Integer_Size);
132
133 Standard_Short_Float_Size : constant Pos :=
134 Set_Targ.Float_Size;
135 Standard_Short_Float_Digits : constant Pos :=
136 Get_Targ.Digits_From_Size
137 (Standard_Short_Float_Size);
138
139 Standard_Float_Size : constant Pos :=
140 Set_Targ.Float_Size;
141 Standard_Float_Digits : constant Pos :=
142 Get_Targ.Digits_From_Size
143 (Standard_Float_Size);
144
145 Standard_Long_Float_Size : constant Pos :=
146 Set_Targ.Double_Size;
147 Standard_Long_Float_Digits : constant Pos :=
148 Get_Targ.Digits_From_Size
149 (Standard_Long_Float_Size);
150
151 Standard_Long_Long_Float_Size : constant Pos :=
152 Set_Targ.Long_Double_Size;
153 Standard_Long_Long_Float_Digits : constant Pos :=
154 Get_Targ.Digits_From_Size
155 (Standard_Long_Long_Float_Size);
156
157 Standard_Character_Size : constant Pos := Set_Targ.Char_Size;
158
159 Standard_Wide_Character_Size : constant Pos := 16;
160 Standard_Wide_Wide_Character_Size : constant Pos := 32;
161 -- Standard wide character sizes
162
163 -- Note: there is no specific control over the representation of
164 -- enumeration types. The convention used is that if an enumeration
165 -- type has fewer than 2**(Character'Size) elements, then the size
166 -- used is Character'Size, otherwise Integer'Size is used.
167
168 -- Similarly, the size of fixed-point types depends on the size of the
169 -- corresponding integer type, which is the smallest predefined integer
170 -- type capable of representing the required range of values.
171
172 -------------------------------------------------
173 -- Target-Dependent Values for Types in System --
174 -------------------------------------------------
175
176 System_Address_Size : constant Pos := Set_Targ.Pointer_Size;
177 -- System.Address'Size (also size of all thin pointers)
178
179 System_Max_Binary_Modulus_Power : constant Pos :=
180 Standard_Long_Long_Integer_Size;
181
182 System_Max_Nonbinary_Modulus_Power : constant Pos := Standard_Integer_Size;
183
184 System_Storage_Unit : constant Pos := Set_Targ.Bits_Per_Unit;
185 System_Word_Size : constant Pos := Set_Targ.Bits_Per_Word;
186
187 System_Tick_Nanoseconds : constant Pos := 1_000_000_000;
188 -- Value of System.Tick in nanoseconds. At the moment, this is a fixed
189 -- constant (with value of 1.0 seconds), but later we should add this
190 -- value to the GCC configuration file so that its value can be made
191 -- configuration dependent.
192
193 -----------------------------------------------------
194 -- Target-Dependent Values for Types in Interfaces --
195 -----------------------------------------------------
196
197 Interfaces_Wchar_T_Size : constant Pos := Set_Targ.Wchar_T_Size;
198
199 ----------------------------------------
200 -- Other Target-Dependent Definitions --
201 ----------------------------------------
202
203 Maximum_Alignment : constant Pos := Set_Targ.Maximum_Alignment;
204 -- The maximum alignment, in storage units, that an object or type may
205 -- require on the target machine.
206
207 System_Allocator_Alignment : constant Pos :=
208 Set_Targ.System_Allocator_Alignment;
209 -- The alignment in storage units of addresses returned by malloc
210
211 Max_Unaligned_Field : constant Pos := Set_Targ.Max_Unaligned_Field;
212 -- The maximum supported size in bits for a field that is not aligned
213 -- on a storage unit boundary.
214
215 Bytes_Big_Endian : Boolean := Set_Targ.Bytes_BE /= 0;
216 -- Important note: for Ada purposes, the important setting is the bytes
217 -- endianness (Bytes_Big_Endian), not the bits value (Bits_Big_Endian).
218 -- This is because Ada bit addressing must be compatible with the byte
219 -- ordering (otherwise we would end up with non-contiguous fields). It
220 -- is rare for the two to be different, but if they are, Bits_Big_Endian
221 -- is relevant only for the generation of instructions with bit numbers,
222 -- and thus relevant only to the back end. Note that this is a variable
223 -- rather than a constant, since it can be modified (flipped) by -gnatd8.
224
225 Target_Short_Enums : constant Boolean := Set_Targ.Short_Enums /= 0;
226 -- True if we are in short enums mode, where foreign convention
227 -- (in particular C and C++) enumeration types will be sized as in Ada,
228 -- using the shortest possibility from 8,16,32 bits, signed or unsigned.
229 -- A zero value means Short_Enums are not in use, and in this case all
230 -- foreign convention enumeration types are given the same size as c int.
231
232 Target_Strict_Alignment : Boolean :=
233 Set_Targ.Strict_Alignment /= 0;
234 -- True if instructions will fail if data is misaligned. Note that this
235 -- is a variable rather than a constant since it can be modified (set to
236 -- True) if the debug flag -gnatd.A is used.
237
238 Target_Double_Float_Alignment : constant Nat :=
239 Set_Targ.Double_Float_Alignment;
240 -- The default alignment of "double" floating-point types, i.e. floating
241 -- point types whose size is equal to 64 bits, or 0 if this alignment is
242 -- not lower than the largest power of 2 multiple of System.Storage_Unit
243 -- that does not exceed either the object size of the type or the maximum
244 -- allowed alignment.
245
246 Target_Double_Scalar_Alignment : constant Nat :=
247 Set_Targ.Double_Scalar_Alignment;
248 -- The default alignment of "double" or larger scalar types, i.e. scalar
249 -- types whose size is greater or equal to 64 bits, or 0 if this alignment
250 -- is not lower than the largest power of 2 multiple of System.Storage_Unit
251 -- that does not exceed either the object size of the type or the maximum
252 -- allowed alignment.
253
254 end Ttypes;