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) 1992-2009, 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; use Get_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 and its companion Ttypef provide definitions of values
  42    --  that describe the properties of the target types. All instances of
  43    --  target dependencies, including the definitions of such packages as
  44    --  Standard and System depend directly or indirectly on the definitions
  45    --  in the Ttypes and Ttypef 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 := Get_Char_Size;
 106    Standard_Short_Short_Integer_Width  : constant Pos :=
 107                            Width_From_Size (Standard_Short_Short_Integer_Size);
 108
 109    Standard_Short_Integer_Size         : constant Pos := Get_Short_Size;
 110    Standard_Short_Integer_Width        : constant Pos :=
 111                            Width_From_Size (Standard_Short_Integer_Size);
 112
 113    Standard_Integer_Size               : constant Pos := Get_Int_Size;
 114    Standard_Integer_Width              : constant Pos :=
 115                            Width_From_Size (Standard_Integer_Size);
 116
 117    Standard_Long_Integer_Size          : constant Pos := Get_Long_Size;
 118    Standard_Long_Integer_Width         : constant Pos :=
 119                            Width_From_Size (Standard_Long_Integer_Size);
 120
 121    Standard_Long_Long_Integer_Size     : constant Pos := Get_Long_Long_Size;
 122    Standard_Long_Long_Integer_Width    : constant Pos :=
 123                            Width_From_Size (Standard_Long_Long_Integer_Size);
 124
 125    Standard_Short_Float_Size           : constant Pos := Get_Float_Size;
 126    Standard_Short_Float_Digits         : constant Pos :=
 127                            Digits_From_Size (Standard_Short_Float_Size);
 128
 129    Standard_Float_Size                 : constant Pos := Get_Float_Size;
 130    Standard_Float_Digits               : constant Pos :=
 131                            Digits_From_Size (Standard_Float_Size);
 132
 133    Standard_Long_Float_Size            : constant Pos := Get_Double_Size;
 134    Standard_Long_Float_Digits          : constant Pos :=
 135                            Digits_From_Size (Standard_Long_Float_Size);
 136
 137    Standard_Long_Long_Float_Size       : constant Pos := Get_Long_Double_Size;
 138    Standard_Long_Long_Float_Digits     : constant Pos :=
 139                            Digits_From_Size (Standard_Long_Long_Float_Size);
 140
 141    Standard_Character_Size             : constant Pos := Get_Char_Size;
 142
 143    Standard_Wide_Character_Size        : constant Pos := 16;
 144    Standard_Wide_Wide_Character_Size   : constant Pos := 32;
 145    --  Standard wide character sizes
 146
 147    --  Note: there is no specific control over the representation of
 148    --  enumeration types. The convention used is that if an enumeration
 149    --  type has fewer than 2**(Character'Size) elements, then the size
 150    --  used is Character'Size, otherwise Integer'Size is used.
 151
 152    --  Similarly, the size of fixed-point types depends on the size of the
 153    --  corresponding integer type, which is the smallest predefined integer
 154    --  type capable of representing the required range of values.
 155
 156    -------------------------------------------------
 157    -- Target-Dependent Values for Types in System --
 158    -------------------------------------------------
 159
 160    System_Address_Size : constant Pos := Get_Pointer_Size;
 161    --  System.Address'Size (also size of all thin pointers)
 162
 163    System_Max_Binary_Modulus_Power : constant Pos :=
 164                                        Standard_Long_Long_Integer_Size;
 165
 166    System_Max_Nonbinary_Modulus_Power : constant Pos := Standard_Integer_Size;
 167
 168    System_Storage_Unit : constant Pos := Get_Bits_Per_Unit;
 169    System_Word_Size    : constant Pos := Get_Bits_Per_Word;
 170
 171    System_Tick_Nanoseconds : constant Pos := 1_000_000_000;
 172    --  Value of System.Tick in nanoseconds. At the moment, this is a fixed
 173    --  constant (with value of 1.0 seconds), but later we should add this
 174    --  value to the GCC configuration file so that its value can be made
 175    --  configuration dependent.
 176
 177    -----------------------------------------------------
 178    -- Target-Dependent Values for Types in Interfaces --
 179    -----------------------------------------------------
 180
 181    Interfaces_Wchar_T_Size : constant Pos := Get_Wchar_T_Size;
 182
 183    ----------------------------------------
 184    -- Other Target-Dependent Definitions --
 185    ----------------------------------------
 186
 187    Maximum_Alignment : constant Pos := Get_Maximum_Alignment;
 188    --  The maximum alignment, in storage units, that an object or
 189    --  type may require on the target machine.
 190
 191    Max_Unaligned_Field : constant Pos := Get_Max_Unaligned_Field;
 192    --  The maximum supported size in bits for a field that is not aligned
 193    --  on a storage unit boundary.
 194
 195    Bytes_Big_Endian : Boolean := Get_Bytes_BE /= 0;
 196    --  Important note: for Ada purposes, the important setting is the bytes
 197    --  endianness (Bytes_Big_Endian), not the bits value (Bits_Big_Endian).
 198    --  This is because Ada bit addressing must be compatible with the byte
 199    --  ordering (otherwise we would end up with non-contiguous fields). It
 200    --  is rare for the two to be different, but if they are, Bits_Big_Endian
 201    --  is relevant only for the generation of instructions with bit numbers,
 202    --  and thus relevant only to the back end. Note that this is a variable
 203    --  rather than a constant, since it can be modified (flipped) by -gnatd8.
 204
 205    Target_Strict_Alignment : Boolean := Get_Strict_Alignment /= 0;
 206    --  True if instructions will fail if data is misaligned
 207
 208    Target_Double_Float_Alignment : Nat := Get_Double_Float_Alignment;
 209    --  The default alignment of "double" floating-point types, i.e. floating
 210    --  point types whose size is equal to 64 bits, or 0 if this alignment is
 211    --  not specifically capped.
 212
 213    Target_Double_Scalar_Alignment : Nat := Get_Double_Scalar_Alignment;
 214    --  The default alignment of "double" or larger scalar types, i.e. scalar
 215    --  types whose size is greater or equal to 64 bits, or 0 if this alignment
 216    --  is not specifically capped.
 217
 218 end Ttypes;