gcc/ada/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) 1992-2023, 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 Set_Targ;
  30
  31 package 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
  65    --  For package System, there is a separate version for each target, with
  66    --  explicit declarations of the required constants.
  67
  68    --  Historical note: Originally we had in mind dealing with target dependent
  69    --  differences by referencing appropriate attributes. Ada 95 already
  70    --  defines most of the required attributes, and GNAT specific attributes
  71    --  were defined to cover the remaining cases (such as Storage_Unit).
  72    --  The additional attributes that have been added to GNAT (Address_Size,
  73    --  Storage_Unit, and Word_Size) are redundant with respect to the
  74    --  corresponding references to System constants. For example in a program,
  75    --  System.Address_Size and Standard'Address_Size yield the same value.
  76    --  These attributes have been retained for compatibility purposes, but
  77    --  serve no purpose at this stage.
  78
  79    --  Note that during compilation there are two versions of package System
  80    --  around. The version that is directly with'ed by compiler packages
  81    --  contains host-dependent definitions, which is what is needed in that
  82    --  case (for example, System.Storage_Unit referenced in the source of the
  83    --  compiler refers to the storage unit of the host, not the target). This
  84    --  means that, like attribute references, any references to constants in
  85    --  package System in the compiler code are suspicious, since it is strange
  86    --  for the compiler to have such host dependencies. If the compiler needs
  87    --  to access the target dependent values of such quantities as Storage_Unit
  88    --  then it should reference the constants in this package (Ttypes), rather
  89    --  than referencing System.Storage_Unit, or Standard'Storage_Unit, both of
  90    --  which would yield the host value.
  91
  92    ---------------------------------------------------
  93    -- Target-Dependent Values for Types in Standard --
  94    ---------------------------------------------------
  95
  96    --  Note: GNAT always supplies all the following integer and float types,
  97    --  but depending on the machine, some of the types may be identical. For
  98    --  example, on some machines, Short_Float may be the same as Float, and
  99    --  Long_Long_Float may be the same as Long_Float.
 100
 101    Standard_Short_Short_Integer_Size  : constant Pos :=
 102                                           Set_Targ.Char_Size;
 103
 104    Standard_Short_Integer_Size        : constant Pos :=
 105                                           Set_Targ.Short_Size;
 106
 107    Standard_Integer_Size              : constant Pos :=
 108                                           Set_Targ.Int_Size;
 109
 110    Standard_Long_Integer_Size         : constant Pos :=
 111                                           Set_Targ.Long_Size;
 112
 113    Standard_Long_Long_Integer_Size    : constant Pos :=
 114                                           Set_Targ.Long_Long_Size;
 115
 116    Standard_Long_Long_Long_Integer_Size : Pos :=
 117                                             Set_Targ.Long_Long_Long_Size;
 118
 119    Standard_Short_Float_Size          : constant Pos :=
 120                                           Set_Targ.Float_Size;
 121
 122    Standard_Float_Size                : constant Pos :=
 123                                           Set_Targ.Float_Size;
 124
 125    Standard_Long_Float_Size           : constant Pos :=
 126                                           Set_Targ.Double_Size;
 127
 128    Standard_Long_Long_Float_Size      : constant Pos :=
 129                                           Set_Targ.Long_Double_Size;
 130
 131    Standard_Character_Size            : constant Pos := Set_Targ.Char_Size;
 132
 133    Standard_Wide_Character_Size       : constant Pos := 16;
 134    Standard_Wide_Wide_Character_Size  : constant Pos := 32;
 135    --  Standard wide character sizes
 136
 137    --  Note: there is no specific control over the representation of
 138    --  enumeration types. The convention used is that if an enumeration
 139    --  type has fewer than 2**(Character'Size) elements, then the size
 140    --  used is Character'Size, otherwise Integer'Size is used.
 141
 142    --  Similarly, the size of fixed-point types depends on the size of the
 143    --  corresponding integer type, which is the smallest predefined integer
 144    --  type capable of representing the required range of values.
 145
 146    -------------------------------------------------
 147    -- Target-Dependent Values for Types in System --
 148    -------------------------------------------------
 149
 150    System_Address_Size : constant Pos := Set_Targ.Pointer_Size;
 151    --  System.Address'Size (also size of all thin pointers)
 152
 153    System_Max_Integer_Size : Pos := Standard_Long_Long_Long_Integer_Size;
 154
 155    System_Max_Binary_Modulus_Power : Pos :=
 156                                        Standard_Long_Long_Long_Integer_Size;
 157
 158    System_Max_Nonbinary_Modulus_Power : constant Pos := Standard_Integer_Size;
 159
 160    System_Storage_Unit : constant Pos := Set_Targ.Bits_Per_Unit;
 161    System_Word_Size    : constant Pos := Set_Targ.Bits_Per_Word;
 162
 163    System_Tick_Nanoseconds : constant Pos := 1_000_000_000;
 164    --  Value of System.Tick in nanoseconds. At the moment, this is a fixed
 165    --  constant (with value of 1.0 seconds), but later we should add this
 166    --  value to the GCC configuration file so that its value can be made
 167    --  configuration dependent.
 168
 169    -----------------------------------------------------
 170    -- Target-Dependent Values for Types in Interfaces --
 171    -----------------------------------------------------
 172
 173    Interfaces_Wchar_T_Size : constant Pos := Set_Targ.Wchar_T_Size;
 174
 175    ----------------------------------------
 176    -- Other Target-Dependent Definitions --
 177    ----------------------------------------
 178
 179    Maximum_Alignment : constant Pos := Set_Targ.Maximum_Alignment;
 180    --  The maximum alignment, in storage units, that an object or type may
 181    --  require on the target machine.
 182
 183    System_Allocator_Alignment : constant Pos :=
 184                                   Set_Targ.System_Allocator_Alignment;
 185    --  The alignment in storage units of addresses returned by malloc
 186
 187    Bytes_Big_Endian : Boolean := Set_Targ.Bytes_BE /= 0;
 188    --  Important note: for Ada purposes, the important setting is the bytes
 189    --  endianness (Bytes_Big_Endian), not the bits value (Bits_Big_Endian).
 190    --  This is because Ada bit addressing must be compatible with the byte
 191    --  ordering (otherwise we would end up with non-contiguous fields). It
 192    --  is rare for the two to be different, but if they are, Bits_Big_Endian
 193    --  is relevant only for the generation of instructions with bit numbers,
 194    --  and thus relevant only to the back end. Note that this is a variable
 195    --  rather than a constant, since it can be modified (flipped) by -gnatd8.
 196
 197    Target_Short_Enums : constant Boolean := Set_Targ.Short_Enums /= 0;
 198    --  True if we are in short enums mode, where foreign convention
 199    --  (in particular C and C++) enumeration types will be sized as in Ada,
 200    --  using the shortest possibility from 8,16,32 bits, signed or unsigned.
 201    --  A zero value means Short_Enums are not in use, and in this case all
 202    --  foreign convention enumeration types are given the same size as c int.
 203
 204    Target_Strict_Alignment : Boolean :=
 205                                Set_Targ.Strict_Alignment /= 0;
 206    --  True if instructions will fail if data is misaligned. Note that this
 207    --  is a variable rather than a constant since it can be modified (set to
 208    --  True) if the debug flag -gnatd.a is used.
 209
 210    Target_Double_Float_Alignment : constant Nat :=
 211                                      Set_Targ.Double_Float_Alignment;
 212    --  The default alignment of "double" floating-point types, i.e. floating
 213    --  point types whose size is equal to 64 bits, or 0 if this alignment is
 214    --  not lower than the largest power of 2 multiple of System.Storage_Unit
 215    --  that does not exceed either the object size of the type or the maximum
 216    --  allowed alignment.
 217
 218    Target_Double_Scalar_Alignment : constant Nat :=
 219                                       Set_Targ.Double_Scalar_Alignment;
 220    --  The default alignment of "double" or larger scalar types, i.e. scalar
 221    --  types whose size is greater or equal to 64 bits, or 0 if this alignment
 222    --  is not lower than the largest power of 2 multiple of System.Storage_Unit
 223    --  that does not exceed either the object size of the type or the maximum
 224    --  allowed alignment.
 225
 226 end Ttypes;