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) 1992-2013, 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, 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 :=
 106                                           Set_Targ.Char_Size;
 107    Standard_Short_Short_Integer_Width : constant Pos :=
 108                                           Get_Targ.Width_From_Size
 109                                            (Standard_Short_Short_Integer_Size);
 110
 111    Standard_Short_Integer_Size        : constant Pos :=
 112                                           Set_Targ.Short_Size;
 113    Standard_Short_Integer_Width       : constant Pos :=
 114                                           Get_Targ.Width_From_Size
 115                                             (Standard_Short_Integer_Size);
 116
 117    Standard_Integer_Size              : constant Pos :=
 118                                           Set_Targ.Int_Size;
 119    Standard_Integer_Width             : constant Pos :=
 120                                           Get_Targ.Width_From_Size
 121                                             (Standard_Integer_Size);
 122
 123    Standard_Long_Integer_Size         : constant Pos :=
 124                                           Set_Targ.Long_Size;
 125    Standard_Long_Integer_Width        : constant Pos :=
 126                                           Get_Targ.Width_From_Size
 127                                             (Standard_Long_Integer_Size);
 128
 129    Standard_Long_Long_Integer_Size    : constant Pos :=
 130                                           Set_Targ.Long_Long_Size;
 131    Standard_Long_Long_Integer_Width   : constant Pos :=
 132                                           Get_Targ.Width_From_Size
 133                                             (Standard_Long_Long_Integer_Size);
 134
 135    Standard_Short_Float_Size          : constant Pos :=
 136                                           Set_Targ.Float_Size;
 137    Standard_Short_Float_Digits        : constant Pos :=
 138                                           Get_Targ.Digits_From_Size
 139                                             (Standard_Short_Float_Size);
 140
 141    Standard_Float_Size                : constant Pos :=
 142                                           Set_Targ.Float_Size;
 143    Standard_Float_Digits              : constant Pos :=
 144                                           Get_Targ.Digits_From_Size
 145                                             (Standard_Float_Size);
 146
 147    Standard_Long_Float_Size           : constant Pos :=
 148                                           Set_Targ.Double_Size;
 149    Standard_Long_Float_Digits         : constant Pos :=
 150                                           Get_Targ.Digits_From_Size
 151                                             (Standard_Long_Float_Size);
 152
 153    Standard_Long_Long_Float_Size      : constant Pos :=
 154                                           Set_Targ.Long_Double_Size;
 155    Standard_Long_Long_Float_Digits    : constant Pos :=
 156                                           Get_Targ.Digits_From_Size
 157                                             (Standard_Long_Long_Float_Size);
 158
 159    Standard_Character_Size            : constant Pos := Set_Targ.Char_Size;
 160
 161    Standard_Wide_Character_Size       : constant Pos := 16;
 162    Standard_Wide_Wide_Character_Size  : constant Pos := 32;
 163    --  Standard wide character sizes
 164
 165    --  Note: there is no specific control over the representation of
 166    --  enumeration types. The convention used is that if an enumeration
 167    --  type has fewer than 2**(Character'Size) elements, then the size
 168    --  used is Character'Size, otherwise Integer'Size is used.
 169
 170    --  Similarly, the size of fixed-point types depends on the size of the
 171    --  corresponding integer type, which is the smallest predefined integer
 172    --  type capable of representing the required range of values.
 173
 174    -------------------------------------------------
 175    -- Target-Dependent Values for Types in System --
 176    -------------------------------------------------
 177
 178    System_Address_Size : constant Pos := Set_Targ.Pointer_Size;
 179    --  System.Address'Size (also size of all thin pointers)
 180
 181    System_Max_Binary_Modulus_Power : constant Pos :=
 182                                        Standard_Long_Long_Integer_Size;
 183
 184    System_Max_Nonbinary_Modulus_Power : constant Pos := Standard_Integer_Size;
 185
 186    System_Storage_Unit : constant Pos := Set_Targ.Bits_Per_Unit;
 187    System_Word_Size    : constant Pos := Set_Targ.Bits_Per_Word;
 188
 189    System_Tick_Nanoseconds : constant Pos := 1_000_000_000;
 190    --  Value of System.Tick in nanoseconds. At the moment, this is a fixed
 191    --  constant (with value of 1.0 seconds), but later we should add this
 192    --  value to the GCC configuration file so that its value can be made
 193    --  configuration dependent.
 194
 195    -----------------------------------------------------
 196    -- Target-Dependent Values for Types in Interfaces --
 197    -----------------------------------------------------
 198
 199    Interfaces_Wchar_T_Size : constant Pos := Set_Targ.Wchar_T_Size;
 200
 201    ----------------------------------------
 202    -- Other Target-Dependent Definitions --
 203    ----------------------------------------
 204
 205    Maximum_Alignment : constant Pos := Set_Targ.Maximum_Alignment;
 206    --  The maximum alignment, in storage units, that an object or type may
 207    --  require on the target machine.
 208
 209    System_Allocator_Alignment : constant Pos :=
 210                                   Set_Targ.System_Allocator_Alignment;
 211    --  The alignment in storage units of addresses returned by malloc
 212
 213    Max_Unaligned_Field : constant Pos := Set_Targ.Max_Unaligned_Field;
 214    --  The maximum supported size in bits for a field that is not aligned
 215    --  on a storage unit boundary.
 216
 217    Bytes_Big_Endian : Boolean := Set_Targ.Bytes_BE /= 0;
 218    --  Important note: for Ada purposes, the important setting is the bytes
 219    --  endianness (Bytes_Big_Endian), not the bits value (Bits_Big_Endian).
 220    --  This is because Ada bit addressing must be compatible with the byte
 221    --  ordering (otherwise we would end up with non-contiguous fields). It
 222    --  is rare for the two to be different, but if they are, Bits_Big_Endian
 223    --  is relevant only for the generation of instructions with bit numbers,
 224    --  and thus relevant only to the back end. Note that this is a variable
 225    --  rather than a constant, since it can be modified (flipped) by -gnatd8.
 226
 227    Target_Strict_Alignment : Boolean :=
 228                                Set_Targ.Strict_Alignment /= 0;
 229    --  True if instructions will fail if data is misaligned. Note that this
 230    --  is a variable rather than a constant since it can be modified (set to
 231    --  True) if the debug flag -gnatd.A is used.
 232
 233    Target_Double_Float_Alignment : constant Nat :=
 234                                      Set_Targ.Double_Float_Alignment;
 235    --  The default alignment of "double" floating-point types, i.e. floating
 236    --  point types whose size is equal to 64 bits, or 0 if this alignment is
 237    --  not lower than the largest power of 2 multiple of System.Storage_Unit
 238    --  that does not exceed either the object size of the type or the maximum
 239    --  allowed alignment.
 240
 241    Target_Double_Scalar_Alignment : constant Nat :=
 242                                       Set_Targ.Double_Scalar_Alignment;
 243    --  The default alignment of "double" or larger scalar types, i.e. scalar
 244    --  types whose size is greater or equal to 64 bits, or 0 if this alignment
 245    --  is not lower than the largest power of 2 multiple of System.Storage_Unit
 246    --  that does not exceed either the object size of the type or the maximum
 247    --  allowed alignment.
 248
 249 end Ttypes;