1------------------------------------------------------------------------------ 2-- -- 3-- GNAT COMPILER COMPONENTS -- 4-- -- 5-- T T Y P E S -- 6-- -- 7-- S p e c -- 8-- -- 9-- Copyright (C) 1992-2003 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 2, 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 COPYING. If not, write -- 19-- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, -- 20-- MA 02111-1307, USA. -- 21-- -- 22-- GNAT was originally developed by the GNAT team at New York University. -- 23-- Extensive contributions were provided by Ada Core Technologies Inc. -- 24-- -- 25------------------------------------------------------------------------------ 26 27-- This package contains constants describing target properties 28 29with Types; use Types; 30with Get_Targ; use Get_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 and its companion Ttypef provide definitions of values 43 -- that describe the properties of the target types. All instances of 44 -- target dependencies, including the definitions of such packages as 45 -- Standard and System depend directly or indirectly on the definitions 46 -- in the Ttypes and Ttypef packages. 47 48 -- In the source of the compiler, references to attributes such as 49 -- Integer'Size will give information regarding the host types (i.e. 50 -- the types within the compiler itself). Such references are therefore 51 -- almost always suspicious (it is hard for example to see that the 52 -- code in the compiler should even be using type Integer very much, 53 -- and certainly this code should not depend on the size of Integer). 54 55 -- On the other hand, it is perfectly reasonable for the compiler to 56 -- require access to the size of type Integer for the target machine, 57 -- e.g. in constructing the internal representation of package Standard. 58 -- For this purpose, instead of referencing the attribute Integer'Size, 59 -- a reference to Ttypes.Standard_Integer_Size will provide the needed 60 -- value for the target type. 61 62 -- Two approaches are used for handling target dependent values in the 63 -- standard library packages. Package Standard is handled specially, 64 -- being constructed internally (by package Stand). Target dependent 65 -- values needed in Stand are obtained by direct reference to Ttypes 66 -- and Ttypef. 67 68 -- For package System, the required constant values are obtained by 69 -- referencing appropriate attributes. Ada 95 already defines most of 70 -- the required attributes, and GNAT specific attributes have been 71 -- defined to cover the remaining cases (such as Storage_Unit). The 72 -- evaluation of these attributes obtains the required target dependent 73 -- values from Ttypes and Ttypef. The additional attributes that have 74 -- been added to GNAT (Address_Size, Storage_Unit, Word_Size, Max_Priority, 75 -- and Max_Interrupt_Priority) are for almost all purposes redundant with 76 -- respect to the corresponding references to System constants. For example 77 -- in a program, System.Address_Size and Standard'Address_Size yield the 78 -- same value. The critical use of the attribute is in writing the System 79 -- declaration of Address_Size which of course cannot refer to itself. By 80 -- this means we achieve complete target independence in the source code 81 -- of package System, i.e. there is only one copy of the source of System 82 -- for all targets. 83 84 -- Note that during compilation there are two versions of package System 85 -- around. The version that is directly WITH'ed by compiler packages 86 -- contains host-dependent definitions, which is what is needed in that 87 -- case (for example, System.Storage_Unit referenced in the source of the 88 -- compiler refers to the storage unit of the host, not the target. This 89 -- means that, like attribute references, any references to constants in 90 -- package System in the compiler code are suspicious, since it is strange 91 -- for the compiler to have such host dependencies. If the compiler needs 92 -- to access the target dependent values of such quantities as Storage_Unit 93 -- then it should reference the constants in this package (Ttypes), rather 94 -- than referencing System.Storage_Unit, or Standard'Storage_Unit, both of 95 -- which would yield the host value. 96 97 --------------------------------------------------- 98 -- Target-Dependent Values for Types in Standard -- 99 --------------------------------------------------- 100 101 -- Note: GNAT always supplies all the following integer and float types, 102 -- but depending on the machine, some of the types may be identical. For 103 -- example, on some machines, Short_Float may be the same as Float, and 104 -- Long_Long_Float may be the same as Long_Float. 105 106 Standard_Short_Short_Integer_Size : constant Pos := Get_Char_Size; 107 Standard_Short_Short_Integer_Width : constant Pos := 108 Width_From_Size (Standard_Short_Short_Integer_Size); 109 110 Standard_Short_Integer_Size : constant Pos := Get_Short_Size; 111 Standard_Short_Integer_Width : constant Pos := 112 Width_From_Size (Standard_Short_Integer_Size); 113 114 Standard_Integer_Size : constant Pos := Get_Int_Size; 115 Standard_Integer_Width : constant Pos := 116 Width_From_Size (Standard_Integer_Size); 117 118 Standard_Long_Integer_Size : constant Pos := Get_Long_Size; 119 Standard_Long_Integer_Width : constant Pos := 120 Width_From_Size (Standard_Long_Integer_Size); 121 122 Standard_Long_Long_Integer_Size : constant Pos := Get_Long_Long_Size; 123 Standard_Long_Long_Integer_Width : constant Pos := 124 Width_From_Size (Standard_Long_Long_Integer_Size); 125 126 Standard_Short_Float_Size : constant Pos := Get_Float_Size; 127 Standard_Short_Float_Digits : constant Pos := 128 Digits_From_Size (Standard_Short_Float_Size); 129 130 Standard_Float_Size : constant Pos := Get_Float_Size; 131 Standard_Float_Digits : constant Pos := 132 Digits_From_Size (Standard_Float_Size); 133 134 Standard_Long_Float_Size : constant Pos := Get_Double_Size; 135 Standard_Long_Float_Digits : constant Pos := 136 Digits_From_Size (Standard_Long_Float_Size); 137 138 Standard_Long_Long_Float_Size : constant Pos := Get_Long_Double_Size; 139 Standard_Long_Long_Float_Digits : constant Pos := 140 Digits_From_Size (Standard_Long_Long_Float_Size); 141 142 Standard_Character_Size : constant Pos := Get_Char_Size; 143 144 Standard_Wide_Character_Size : constant Pos := 16; 145 -- The Standard.Wide_Character type is special in the sense that 146 -- it is not defined in terms of its corresponding C type (wchar_t). 147 -- Unfortunately this makes the representation of Wide_Character 148 -- incompatible with the C wchar_t type. 149 -- ??? This is required by the RM or backward compatibility 150 151 -- Note: there is no specific control over the representation of 152 -- enumeration types. The convention used is that if an enumeration 153 -- type has fewer than 2**(Character'Size) elements, then the size 154 -- used is Character'Size, otherwise Integer'Size is used. 155 156 -- Similarly, the size of fixed-point types depends on the size of the 157 -- corresponding integer type, which is the smallest predefined integer 158 -- type capable of representing the required range of values. 159 160 ------------------------------------------------- 161 -- Target-Dependent Values for Types in System -- 162 ------------------------------------------------- 163 164 System_Address_Size : constant Pos := Get_Pointer_Size; 165 -- System.Address'Size (also size of all thin pointers) 166 167 System_Max_Binary_Modulus_Power : constant Pos := 168 Standard_Long_Long_Integer_Size; 169 170 System_Max_Nonbinary_Modulus_Power : constant Pos := 171 Standard_Integer_Size - 1; 172 173 System_Storage_Unit : constant Pos := Get_Bits_Per_Unit; 174 System_Word_Size : constant Pos := Get_Bits_Per_Word; 175 176 System_Tick_Nanoseconds : constant Pos := 1_000_000_000; 177 -- Value of System.Tick in nanoseconds. At the moment, this is a fixed 178 -- constant (with value of 1.0 seconds), but later we should add this 179 -- value to the GCC configuration file so that its value can be made 180 -- configuration dependent. 181 182 ----------------------------------------------------- 183 -- Target-Dependent Values for Types in Interfaces -- 184 ----------------------------------------------------- 185 186 Interfaces_Wchar_T_Size : constant Pos := Get_Wchar_T_Size; 187 188 ---------------------------------------- 189 -- Other Target-Dependent Definitions -- 190 ---------------------------------------- 191 192 Maximum_Alignment : constant Pos := Get_Maximum_Alignment; 193 -- The maximum alignment, in storage units, that an object or 194 -- type may require on the target machine. 195 196 Max_Unaligned_Field : constant Pos := Get_Max_Unaligned_Field; 197 -- The maximum supported size in bits for a field that is not aligned 198 -- on a storage unit boundary. 199 200 Bytes_Big_Endian : Boolean := Get_Bytes_BE /= 0; 201 -- Important note: for Ada purposes, the important setting is the bytes 202 -- endianness (Bytes_Big_Endian), not the bits value (Bits_Big_Endian). 203 -- This is because Ada bit addressing must be compatible with the byte 204 -- ordering (otherwise we would end up with non-contiguous fields). It 205 -- is rare for the two to be different, but if they are, Bits_Big_Endian 206 -- is relevant only for the generation of instructions with bit numbers, 207 -- and thus relevant only to the back end. Note that this is a variable 208 -- rather than a constant, since it can be modified (flipped) by -gnatd8. 209 210 Target_Strict_Alignment : Boolean := Get_Strict_Alignment /= 0; 211 -- True if instructions will fail if data is misaligned 212 213end Ttypes; 214