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 --                                                                          --
  10 --          Copyright (C) 1992-2002 Free Software Foundation, Inc.          --
  11 --                                                                          --
  12 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  13 -- terms of the  GNU General Public License as published  by the Free Soft- --
  14 -- ware  Foundation;  either version 2,  or (at your option) any later ver- --
  15 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  16 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  17 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  18 -- for  more details.  You should have  received  a copy of the GNU General --
  19 -- Public License  distributed with GNAT;  see file COPYING.  If not, write --
  20 -- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
  21 -- MA 02111-1307, USA.                                                      --
  22 --                                                                          --
  23 -- GNAT was originally developed  by the GNAT team at  New York University. --
  24 -- It is now maintained by Ada Core Technologies Inc (http://www.gnat.com). --
  25 --                                                                          --
  26 ------------------------------------------------------------------------------
  27
  28 --  This package contains constants describing target properties
  29
  30 with Types;    use Types;
  31 with Get_Targ; use Get_Targ;
  32
  33 package Ttypes is
  34
  35    ------------------------------
  36    -- Host/Target Dependencies --
  37    ------------------------------
  38
  39    --  It is vital to maintain a clear distinction between properties of
  40    --  types on the host and types on the target, since in the general
  41    --  case of a cross-compiler these will be different.
  42
  43    --  This package and its companion Ttypef provide definitions of values
  44    --  that describe the properties of the target types. All instances of
  45    --  target dependencies, including the definitions of such packages as
  46    --  Standard and System depend directly or indirectly on the definitions
  47    --  in the Ttypes and Ttypef packages.
  48
  49    --  In the source of the compiler, references to attributes such as
  50    --  Integer'Size will give information regarding the host types (i.e.
  51    --  the types within the compiler itself). Such references are therefore
  52    --  almost always suspicious (it is hard for example to see that the
  53    --  code in the compiler should even be using type Integer very much,
  54    --  and certainly this code should not depend on the size of Integer).
  55
  56    --  On the other hand, it is perfectly reasonable for the compiler to
  57    --  require access to the size of type Integer for the target machine,
  58    --  e.g. in constructing the internal representation of package Standard.
  59    --  For this purpose, instead of referencing the attribute Integer'Size,
  60    --  a reference to Ttypes.Standard_Integer_Size will provide the needed
  61    --  value for the target type.
  62
  63    --  Two approaches are used for handling target dependent values in the
  64    --  standard library packages. Package Standard is handled specially,
  65    --  being constructed internally (by package Stand). Target dependent
  66    --  values needed in Stand are obtained by direct reference to Ttypes
  67    --  and Ttypef.
  68
  69    --  For package System, the required constant values are obtained by
  70    --  referencing appropriate attributes. Ada 95 already defines most of
  71    --  the required attributes, and GNAT specific attributes have been
  72    --  defined to cover the remaining cases (such as Storage_Unit). The
  73    --  evaluation of these attributes obtains the required target dependent
  74    --  values from Ttypes and Ttypef. The additional attributes that have
  75    --  been added to GNAT (Address_Size, Storage_Unit, Word_Size, Max_Priority,
  76    --  and Max_Interrupt_Priority) are for almost all purposes redundant with
  77    --  respect to the corresponding references to System constants. For example
  78    --  in a program, System.Address_Size and Standard'Address_Size yield the
  79    --  same value. The critical use of the attribute is in writing the System
  80    --  declaration of Address_Size which of course cannot refer to itself. By
  81    --  this means we achieve complete target independence in the source code
  82    --  of package System, i.e. there is only one copy of the source of System
  83    --  for all targets.
  84
  85    --  Note that during compilation there are two versions of package System
  86    --  around. The version that is directly WITH'ed by compiler packages
  87    --  contains host-dependent definitions, which is what is needed in that
  88    --  case (for example, System.Storage_Unit referenced in the source of the
  89    --  compiler refers to the storage unit of the host, not the target. This
  90    --  means that, like attribute references, any references to constants in
  91    --  package System in the compiler code are suspicious, since it is strange
  92    --  for the compiler to have such host dependencies. If the compiler needs
  93    --  to access the target dependent values of such quantities as Storage_Unit
  94    --  then it should reference the constants in this package (Ttypes), rather
  95    --  than referencing System.Storage_Unit, or Standard'Storage_Unit, both of
  96    --  which would yield the host value.
  97
  98    ---------------------------------------------------
  99    -- Target-Dependent Values for Types in Standard --
 100    ---------------------------------------------------
 101
 102    --  Note: GNAT always supplies all the following integer and float types,
 103    --  but depending on the machine, some of the types may be identical. For
 104    --  example, on some machines, Short_Float may be the same as Float, and
 105    --  Long_Long_Float may be the same as Long_Float.
 106
 107    Standard_Short_Short_Integer_Size   : constant Pos := Get_Char_Size;
 108    Standard_Short_Short_Integer_Width  : constant Pos :=
 109                            Width_From_Size (Standard_Short_Short_Integer_Size);
 110
 111    Standard_Short_Integer_Size         : constant Pos := Get_Short_Size;
 112    Standard_Short_Integer_Width        : constant Pos :=
 113                            Width_From_Size (Standard_Short_Integer_Size);
 114
 115    Standard_Integer_Size               : constant Pos := Get_Int_Size;
 116    Standard_Integer_Width              : constant Pos :=
 117                            Width_From_Size (Standard_Integer_Size);
 118
 119    Standard_Long_Integer_Size          : constant Pos := Get_Long_Size;
 120    Standard_Long_Integer_Width         : constant Pos :=
 121                            Width_From_Size (Standard_Long_Integer_Size);
 122
 123    Standard_Long_Long_Integer_Size     : constant Pos := Get_Long_Long_Size;
 124    Standard_Long_Long_Integer_Width    : constant Pos :=
 125                            Width_From_Size (Standard_Long_Long_Integer_Size);
 126
 127    Standard_Short_Float_Size           : constant Pos := Get_Float_Size;
 128    Standard_Short_Float_Digits         : constant Pos :=
 129                            Digits_From_Size (Standard_Short_Float_Size);
 130
 131    Standard_Float_Size                 : constant Pos := Get_Float_Size;
 132    Standard_Float_Digits               : constant Pos :=
 133                            Digits_From_Size (Standard_Float_Size);
 134
 135    Standard_Long_Float_Size            : constant Pos := Get_Double_Size;
 136    Standard_Long_Float_Digits          : constant Pos :=
 137                            Digits_From_Size (Standard_Long_Float_Size);
 138
 139    Standard_Long_Long_Float_Size       : constant Pos := Get_Long_Double_Size;
 140    Standard_Long_Long_Float_Digits     : constant Pos :=
 141                            Digits_From_Size (Standard_Long_Long_Float_Size);
 142
 143    Standard_Character_Size             : constant Pos := Get_Char_Size;
 144
 145    Standard_Wide_Character_Size        : constant Pos := 16;
 146    --  The Standard.Wide_Character type is special in the sense that
 147    --  it is not defined in terms of its corresponding C type (wchar_t).
 148    --  Unfortunately this makes the representation of Wide_Character
 149    --  incompatible with the C wchar_t type.
 150    --  ??? This is required by the RM or backward compatibility
 151
 152    --  Note: there is no specific control over the representation of
 153    --  enumeration types. The convention used is that if an enumeration
 154    --  type has fewer than 2**(Character'Size) elements, then the size
 155    --  used is Character'Size, otherwise Integer'Size is used.
 156
 157    --  Similarly, the size of fixed-point types depends on the size of the
 158    --  corresponding integer type, which is the smallest predefined integer
 159    --  type capable of representing the required range of values.
 160
 161    -------------------------------------------------
 162    -- Target-Dependent Values for Types in System --
 163    -------------------------------------------------
 164
 165    System_Address_Size : constant Pos := Get_Pointer_Size;
 166    --  System.Address'Size (also size of all thin pointers)
 167
 168    System_Max_Binary_Modulus_Power    : constant Pos :=
 169                                           Standard_Long_Long_Integer_Size;
 170
 171    System_Max_Nonbinary_Modulus_Power : constant Pos :=
 172                                           Standard_Integer_Size - 1;
 173
 174    System_Storage_Unit : constant Pos := Get_Bits_Per_Unit;
 175    System_Word_Size    : constant Pos := Get_Bits_Per_Word;
 176
 177    System_Tick_Nanoseconds : constant Pos := 1_000_000_000;
 178    --  Value of System.Tick in nanoseconds. At the moment, this is a fixed
 179    --  constant (with value of 1.0 seconds), but later we should add this
 180    --  value to the GCC configuration file so that its value can be made
 181    --  configuration dependent.
 182
 183    -----------------------------------------------------
 184    -- Target-Dependent Values for Types in Interfaces --
 185    -----------------------------------------------------
 186
 187    Interfaces_Wchar_T_Size : constant Pos := Get_Wchar_T_Size;
 188
 189    ----------------------------------------
 190    -- Other Target-Dependent Definitions --
 191    ----------------------------------------
 192
 193    Maximum_Alignment : constant Pos := Get_Maximum_Alignment;
 194    --  The maximum alignment, in storage units, that an object or
 195    --  type may require on the target machine.
 196
 197    Bytes_Big_Endian : Boolean := Get_Bytes_BE /= 0;
 198    --  Important note: for Ada purposes, the important setting is the bytes
 199    --  endianness (Bytes_Big_Endian), not the bits value (Bits_Big_Endian).
 200    --  This is because Ada bit addressing must be compatible with the byte
 201    --  ordering (otherwise we would end up with non-contiguous fields). It
 202    --  is rare for the two to be different, but if they are, Bits_Big_Endian
 203    --  is relevant only for the generation of instructions with bit numbers,
 204    --  and thus relevant only to the back end. Note that this is a variable
 205    --  rather than a constant, since it can be modified (flipped) by -gnatd8.
 206
 207    Target_Strict_Alignment : Boolean := Get_Strict_Alignment /= 0;
 208    --  True if instructions will fail if data is misaligned
 209
 210 end Ttypes;