gcc/ada/types.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT COMPILER COMPONENTS                         --
   4 --                                                                          --
   5 --                                T Y P E S                                 --
   6 --                                                                          --
   7 --                                 S p e c                                  --
   8 --                                                                          --
   9 --                            $Revision: 1.2 $
  10 --                                                                          --
  11 --          Copyright (C) 1992-2001 Free Software Foundation, Inc.          --
  12 --                                                                          --
  13 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  14 -- terms of the  GNU General Public License as published  by the Free Soft- --
  15 -- ware  Foundation;  either version 2,  or (at your option) any later ver- --
  16 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  17 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  18 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  19 -- for  more details.  You should have  received  a copy of the GNU General --
  20 -- Public License  distributed with GNAT;  see file COPYING.  If not, write --
  21 -- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
  22 -- MA 02111-1307, USA.                                                      --
  23 --                                                                          --
  24 -- As a special exception,  if other files  instantiate  generics from this --
  25 -- unit, or you link  this unit with other files  to produce an executable, --
  26 -- this  unit  does not  by itself cause  the resulting  executable  to  be --
  27 -- covered  by the  GNU  General  Public  License.  This exception does not --
  28 -- however invalidate  any other reasons why  the executable file  might be --
  29 -- covered by the  GNU Public License.                                      --
  30 --                                                                          --
  31 -- GNAT was originally developed  by the GNAT team at  New York University. --
  32 -- It is now maintained by Ada Core Technologies Inc (http://www.gnat.com). --
  33 --                                                                          --
  34 ------------------------------------------------------------------------------
  35
  36 with Unchecked_Deallocation;
  37
  38 package Types is
  39 pragma Preelaborate (Types);
  40
  41 --  This package contains host independent type definitions which are used
  42 --  in more than one unit in the compiler. They are gathered here for easy
  43 --  reference, though in some cases the full description is found in the
  44 --  relevant module which implements the definition. The main reason that
  45 --  they are not in their "natural" specs is that this would cause a lot of
  46 --  inter-spec dependencies, and in particular some awkward circular
  47 --  dependencies would have to be dealt with.
  48
  49 --  WARNING: There is a C version of this package. Any changes to this
  50 --  source file must be properly reflected in the C header file a-types.h
  51
  52 --  Note: the declarations in this package reflect an expectation that the
  53 --  host machine has an efficient integer base type with a range at least
  54 --  32 bits 2s-complement. If there are any machines for which this is not
  55 --  a correct assumption, a significant number of changes will be required!
  56
  57    -------------------------------
  58    -- General Use Integer Types --
  59    -------------------------------
  60
  61    type Int is range -2 ** 31 .. +2 ** 31 - 1;
  62    --  Signed 32-bit integer
  63
  64    type Dint is range -2 ** 63 .. +2 ** 63 - 1;
  65    --  Double length (64-bit) integer
  66
  67    subtype Nat is Int range 0 .. Int'Last;
  68    --  Non-negative Int values
  69
  70    subtype Pos is Int range 1 .. Int'Last;
  71    --  Positive Int values
  72
  73    type Word is mod 2 ** 32;
  74    --  Unsigned 32-bit integer
  75
  76    type Short is range -32768 .. +32767;
  77    for Short'Size use 16;
  78    --  16-bit signed integer
  79
  80    type Byte is mod 2 ** 8;
  81    for Byte'Size use 8;
  82    --  8-bit unsigned integer
  83
  84    type size_t is mod 2 ** Standard'Address_Size;
  85    --  Memory size value, for use in calls to C routines
  86
  87    --------------------------------------
  88    -- 8-Bit Character and String Types --
  89    --------------------------------------
  90
  91    --  We use Standard.Character and Standard.String freely, since we are
  92    --  compiling ourselves, and we properly implement the required 8-bit
  93    --  character code as required in Ada 95. This section defines a few
  94    --  general use constants and subtypes.
  95
  96    EOF : constant Character := ASCII.SUB;
  97    --  The character SUB (16#1A#) is used in DOS and other systems derived
  98    --  from DOS (OS/2, NT etc) to signal the end of a text file. Internally
  99    --  all source files are ended by an EOF character, even on Unix systems.
 100    --  An EOF character acts as the end of file only as the last character
 101    --  of a source buffer, in any other position, it is treated as a blank
 102    --  if it appears between tokens, and as an illegal character otherwise.
 103    --  This makes life easier dealing with files that originated from DOS,
 104    --  including concatenated files with interspersed EOF characters.
 105
 106    subtype Graphic_Character is Character range ' ' .. '~';
 107    --  Graphic characters, as defined in ARM
 108
 109    subtype Line_Terminator is Character range ASCII.LF .. ASCII.CR;
 110    --  Line terminator characters (LF, VT, FF, CR)
 111
 112    subtype Upper_Half_Character is
 113      Character range Character'Val (16#80#) .. Character'Val (16#FF#);
 114    --  Characters with the upper bit set
 115
 116    type Character_Ptr is access all Character;
 117    type String_Ptr    is access all String;
 118    --  Standard character and string pointers
 119
 120    procedure Free is new Unchecked_Deallocation (String, String_Ptr);
 121    --  Procedure for freeing dynamically allocated String values
 122
 123    subtype Word_Hex_String is String (1 .. 8);
 124    --  Type used to represent Word value as 8 hex digits, with lower case
 125    --  letters for the alphabetic cases.
 126
 127    function Get_Hex_String (W : Word) return Word_Hex_String;
 128    --  Convert word value to 8-character hex string
 129
 130    -----------------------------------------
 131    -- Types Used for Text Buffer Handling --
 132    -----------------------------------------
 133
 134    --  We can't use type String for text buffers, since we must use the
 135    --  standard 32-bit integer as an index value, since we count on all
 136    --  index values being the same size.
 137
 138    type Text_Ptr is new Int;
 139    --  Type used for subscripts in text buffer
 140
 141    type Text_Buffer is array (Text_Ptr range <>) of Character;
 142    --  Text buffer used to hold source file or library information file
 143
 144    type Text_Buffer_Ptr is access all Text_Buffer;
 145    --  Text buffers for input files are allocated dynamically and this type
 146    --  is used to reference these text buffers.
 147
 148    procedure Free is new Unchecked_Deallocation (Text_Buffer, Text_Buffer_Ptr);
 149    --  Procedure for freeing dynamically allocated text buffers
 150
 151    ------------------------------------------
 152    -- Types Used for Source Input Handling --
 153    ------------------------------------------
 154
 155    type Logical_Line_Number is range 0 .. Int'Last;
 156    for Logical_Line_Number'Size use 32;
 157    --  Line number type, used for storing logical line numbers (i.e. line
 158    --  numbers that include effects of any Source_Reference pragmas in the
 159    --  source file). The value zero indicates a line containing a source
 160    --  reference pragma.
 161
 162    No_Line_Number : constant Logical_Line_Number := 0;
 163    --  Special value used to indicate no line number
 164
 165    type Physical_Line_Number is range 1 .. Int'Last;
 166    for Physical_Line_Number'Size use 32;
 167    --  Line number type, used for storing physical line numbers (i.e.
 168    --  line numbers in the physical file being compiled, unaffected by
 169    --  the presence of source reference pragmas.
 170
 171    type Column_Number is range 0 .. 32767;
 172    for Column_Number'Size use 16;
 173    --  Column number (assume that 2**15 is large enough, see declaration
 174    --  of Hostparm.Max_Line_Length)
 175
 176    No_Column_Number : constant Column_Number := 0;
 177    --  Special value used to indicate no column number
 178
 179    subtype Source_Buffer is Text_Buffer;
 180    --  Type used to store text of a source file . The buffer for the main
 181    --  source (the source specified on the command line) has a lower bound
 182    --  starting at zero. Subsequent subsidiary sources have lower bounds
 183    --  which are one greater than the previous upper bound.
 184
 185    subtype Big_Source_Buffer is Text_Buffer (0 .. Text_Ptr'Last);
 186    --  This is a virtual type used as the designated type of the access
 187    --  type Source_Buffer_Ptr, see Osint.Read_Source_File for details.
 188
 189    type Source_Buffer_Ptr is access all Big_Source_Buffer;
 190    --  Pointer to source buffer. We use virtual origin addressing for
 191    --  source buffers, with thin pointers. The pointer points to a virtual
 192    --  instance of type Big_Source_Buffer, where the actual type is in fact
 193    --  of type Source_Buffer. The address is adjusted so that the virtual
 194    --  origin addressing works correctly. See Osint.Read_Source_Buffer for
 195    --  further details.
 196
 197    subtype Source_Ptr is Text_Ptr;
 198    --  Type used to represent a source location, which is a subscript of a
 199    --  character in the source buffer. As noted above, diffferent source
 200    --  buffers have different ranges, so it is possible to tell from a
 201    --  Source_Ptr value which source it refers to. Note that negative numbers
 202    --  are allowed to accommodate the following special values.
 203
 204    No_Location : constant Source_Ptr := -1;
 205    --  Value used to indicate no source position set in a node
 206
 207    Standard_Location : constant Source_Ptr := -2;
 208    --  Used for all nodes in the representation of package Standard other
 209    --  than nodes representing the contents of Standard.ASCII. Note that
 210    --  testing for <= Standard_Location tests for both Standard_Location
 211    --  and for Standard_ASCII_Location.
 212
 213    Standard_ASCII_Location : constant Source_Ptr := -3;
 214    --  Used for all nodes in the presentation of package Standard.ASCII
 215
 216    First_Source_Ptr : constant Source_Ptr := 0;
 217    --  Starting source pointer index value for first source program
 218
 219    -------------------------------------
 220    -- Range Definitions for Tree Data --
 221    -------------------------------------
 222
 223    --  The tree has fields that can hold any of the following types:
 224
 225    --    Pointers to other tree nodes (type Node_Id)
 226    --    List pointers (type List_Id)
 227    --    Element list pointers (type Elist_Id)
 228    --    Names (type Name_Id)
 229    --    Strings (type String_Id)
 230    --    Universal integers (type Uint)
 231    --    Universal reals (type Ureal)
 232    --    Character codes (type Char_Code stored with a bias)
 233
 234    --  In most contexts, the strongly typed interface determines which of
 235    --  these types is present. However, there are some situations (involving
 236    --  untyped traversals of the tree), where it is convenient to be easily
 237    --  able to distinguish these values. The underlying representation in all
 238    --  cases is an integer type Union_Id, and we ensure that the range of
 239    --  the various possible values for each of the above types is disjoint
 240    --  so that this distinction is possible.
 241
 242    type Union_Id is new Int;
 243    --  The type in the tree for a union of possible ID values
 244
 245    --  Note: it is also helpful for debugging purposes to make these ranges
 246    --  distinct. If a bug leads to misidentification of a value, then it will
 247    --  typically result in an out of range value and a Constraint_Error.
 248
 249    List_Low_Bound : constant := -100_000_000;
 250    --  The List_Id values are subscripts into an array of list headers which
 251    --  has List_Low_Bound as its lower bound. This value is chosen so that all
 252    --  List_Id values are negative, and the value zero is in the range of both
 253    --  List_Id and Node_Id values (see further description below).
 254
 255    List_High_Bound : constant := 0;
 256    --  Maximum List_Id subscript value. This allows up to 100 million list
 257    --  Id values, which is in practice infinite, and there is no need to
 258    --  check the range. The range overlaps the node range by one element
 259    --  (with value zero), which is used both for the Empty node, and for
 260    --  indicating no list. The fact that the same value is used is convenient
 261    --  because it means that the default value of Empty applies to both nodes
 262    --  and lists, and also is more efficient to test for.
 263
 264    Node_Low_Bound : constant := 0;
 265    --  The tree Id values start at zero, because we use zero for Empty (to
 266    --  allow a zero test for Empty). Actual tree node subscripts start at 0
 267    --  since Empty is a legitimate node value.
 268
 269    Node_High_Bound : constant := 099_999_999;
 270    --  Maximum number of nodes that can be allocated is 100 million, which
 271    --  is in practice infinite, and there is no need to check the range.
 272
 273    Elist_Low_Bound : constant := 100_000_000;
 274    --  The Elist_Id values are subscripts into an array of elist headers which
 275    --  has Elist_Low_Bound as its lower bound.
 276
 277    Elist_High_Bound : constant := 199_999_999;
 278    --  Maximum Elist_Id subscript value. This allows up to 100 million Elists,
 279    --  which is in practice infinite and there is no need to check the range.
 280
 281    Elmt_Low_Bound : constant := 200_000_000;
 282    --  Low bound of element Id values. The use of these values is internal to
 283    --  the Elists package, but the definition of the range is included here
 284    --  since it must be disjoint from other Id values. The Elmt_Id values are
 285    --  subscripts into an array of list elements which has this as lower bound.
 286
 287    Elmt_High_Bound : constant := 299_999_999;
 288    --  Upper bound of Elmt_Id values. This allows up to 100 million element
 289    --  list members, which is in practice infinite (no range check needed).
 290
 291    Names_Low_Bound : constant := 300_000_000;
 292    --  Low bound for name Id values
 293
 294    Names_High_Bound : constant := 399_999_999;
 295    --  Maximum number of names that can be allocated is 100 million, which is
 296    --  in practice infinite and there is no need to check the range.
 297
 298    Strings_Low_Bound : constant := 400_000_000;
 299    --  Low bound for string Id values
 300
 301    Strings_High_Bound : constant := 499_999_999;
 302    --  Maximum number of strings that can be allocated is 100 million, which
 303    --  is in practice infinite and there is no need to check the range.
 304
 305    Ureal_Low_Bound : constant := 500_000_000;
 306    --  Low bound for Ureal values.
 307
 308    Ureal_High_Bound : constant := 599_999_999;
 309    --  Maximum number of Ureal values stored is 100_000_000 which is in
 310    --  practice infinite so that no check is required.
 311
 312    Uint_Low_Bound : constant := 600_000_000;
 313    --  Low bound for Uint values.
 314
 315    Uint_Table_Start : constant := 2_000_000_000;
 316    --  Location where table entries for universal integers start (see
 317    --  Uintp spec for details of the representation of Uint values).
 318
 319    Uint_High_Bound : constant := 2_099_999_999;
 320    --  The range of Uint values is very large, since a substantial part
 321    --  of this range is used to store direct values, see Uintp for details.
 322
 323    Char_Code_Bias : constant := 2_100_000_000;
 324    --  A bias value added to character code values stored in the tree which
 325    --  ensures that they have different values from any of the above types.
 326
 327    --  The following subtype definitions are used to provide convenient names
 328    --  for membership tests on Int values to see what data type range they
 329    --  lie in. Such tests appear only in the lowest level packages.
 330
 331    subtype List_Range      is Union_Id
 332      range List_Low_Bound   .. List_High_Bound;
 333
 334    subtype Node_Range      is Union_Id
 335      range Node_Low_Bound   .. Node_High_Bound;
 336
 337    subtype Elist_Range     is Union_Id
 338      range Elist_Low_Bound  .. Elist_High_Bound;
 339
 340    subtype Elmt_Range      is Union_Id
 341      range Elmt_Low_Bound   .. Elmt_High_Bound;
 342
 343    subtype Names_Range     is Union_Id
 344      range Names_Low_Bound   .. Names_High_Bound;
 345
 346    subtype Strings_Range   is Union_Id
 347      range Strings_Low_Bound .. Strings_High_Bound;
 348
 349    subtype Uint_Range      is Union_Id
 350      range Uint_Low_Bound    .. Uint_High_Bound;
 351
 352    subtype Ureal_Range     is Union_Id
 353      range Ureal_Low_Bound    .. Ureal_High_Bound;
 354
 355    subtype Char_Code_Range is Union_Id
 356      range Char_Code_Bias    .. Char_Code_Bias + 2**16 - 1;
 357
 358    -----------------------------
 359    -- Types for Namet Package --
 360    -----------------------------
 361
 362    --  Name_Id values are used to identify entries in the names table. Except
 363    --  for the special values No_Name, and Error_Name, they are subscript
 364    --  values for the Names table defined in package Namet.
 365
 366    --  Note that with only a few exceptions, which are clearly documented, the
 367    --  type Name_Id should be regarded as a private type. In particular it is
 368    --  never appropriate to perform arithmetic operations using this type.
 369
 370    type Name_Id is range Names_Low_Bound .. Names_High_Bound;
 371    for Name_Id'Size use 32;
 372    --  Type used to identify entries in the names table
 373
 374    No_Name : constant Name_Id := Names_Low_Bound;
 375    --  The special Name_Id value No_Name is used in the parser to indicate
 376    --  a situation where no name is present (e.g. on a loop or block).
 377
 378    Error_Name : constant Name_Id := Names_Low_Bound +  1;
 379    --  The special Name_Id value Error_Name is used in the parser to
 380    --  indicate that some kind of error was encountered in scanning out
 381    --  the relevant name, so it does not have a representable label.
 382
 383    First_Name_Id : constant Name_Id := Names_Low_Bound + 2;
 384    --  Subscript of first entry in names table
 385
 386    ----------------------------
 387    -- Types for Atree Package --
 388    ----------------------------
 389
 390    --  Node_Id values are used to identify nodes in the tree. They are
 391    --  subscripts into the Node table declared in package Tree. Note that
 392    --  the special values Empty and Error are subscripts into this table,
 393    --  See package Atree for further details.
 394
 395    type Node_Id is range Node_Low_Bound .. Node_High_Bound;
 396    --  Type used to identify nodes in the tree
 397
 398    subtype Entity_Id is Node_Id;
 399    --  A synonym for node types, used in the entity package to refer to
 400    --  nodes that are entities (i.e. nodes with an Nkind of N_Defining_xxx)
 401    --  All such nodes are extended nodes and these are the only extended
 402    --  nodes, so that in practice entity and extended nodes are synonymous.
 403
 404    subtype Node_Or_Entity_Id is Node_Id;
 405    --  A synonym for node types, used in cases where a given value may be used
 406    --  to represent either a node or an entity. We like to minimize such uses
 407    --  for obvious reasons of logical type consistency, but where such uses
 408    --  occur, they should be documented by use of this type.
 409
 410    Empty : constant Node_Id := Node_Low_Bound;
 411    --  Used to indicate null node. A node is actually allocated with this
 412    --  Id value, so that Nkind (Empty) = N_Empty. Note that Node_Low_Bound
 413    --  is zero, so Empty = No_List = zero.
 414
 415    Empty_List_Or_Node : constant := 0;
 416    --  This constant is used in situations (e.g. initializing empty fields)
 417    --  where the value set will be used to represent either an empty node
 418    --  or a non-existent list, depending on the context.
 419
 420    Error : constant Node_Id := Node_Low_Bound + 1;
 421    --  Used to indicate that there was an error in the source program. A node
 422    --  is actually allocated at this address, so that Nkind (Error) = N_Error.
 423
 424    Empty_Or_Error : constant Node_Id := Error;
 425    --  Since Empty and Error are the first two Node_Id values, the test for
 426    --  N <= Empty_Or_Error tests to see if N is Empty or Error. This definition
 427    --  provides convenient self-documentation for such tests.
 428
 429    First_Node_Id  : constant Node_Id := Node_Low_Bound;
 430    --  Subscript of first allocated node. Note that Empty and Error are both
 431    --  allocated nodes, whose Nkind fields can be accessed without error.
 432
 433    ------------------------------
 434    -- Types for Nlists Package --
 435    ------------------------------
 436
 437    --  List_Id values are used to identify node lists in the tree. They are
 438    --  subscripts into the Lists table declared in package Tree. Note that
 439    --  the special value Error_List is a subscript in this table, but the
 440    --  value No_List is *not* a valid subscript, and any attempt to apply
 441    --  list operations to No_List will cause a (detected) error.
 442
 443    type List_Id is range List_Low_Bound .. List_High_Bound;
 444    --  Type used to identify a node list
 445
 446    No_List : constant List_Id := List_High_Bound;
 447    --  Used to indicate absence of a list. Note that the value is zero, which
 448    --  is the same as Empty, which is helpful in intializing nodes where a
 449    --  value of zero can represent either an empty node or an empty list.
 450
 451    Error_List : constant List_Id := List_Low_Bound;
 452    --  Used to indicate that there was an error in the source program in a
 453    --  context which would normally require a list. This node appears to be
 454    --  an empty list to the list operations (a null list is actually allocated
 455    --  which has this Id value).
 456
 457    First_List_Id : constant List_Id := Error_List;
 458    --  Subscript of first allocated list header
 459
 460    ------------------------------
 461    -- Types for Elists Package --
 462    ------------------------------
 463
 464    --  Element list Id values are used to identify element lists stored in
 465    --  the tree (see package Tree for further details). They are formed by
 466    --  adding a bias (Element_List_Bias) to subscript values in the same
 467    --  array that is used for node list headers.
 468
 469    type Elist_Id is range Elist_Low_Bound .. Elist_High_Bound;
 470    --  Type used to identify an element list (Elist header table subscript)
 471
 472    No_Elist : constant Elist_Id := Elist_Low_Bound;
 473    --  Used to indicate absense of an element list. Note that this is not
 474    --  an actual Elist header, so element list operations on this value
 475    --  are not valid.
 476
 477    First_Elist_Id : constant Elist_Id := No_Elist + 1;
 478    --  Subscript of first allocated Elist header.
 479
 480    --  Element Id values are used to identify individual elements of an
 481    --  element list (see package Elists for further details).
 482
 483    type Elmt_Id is range Elmt_Low_Bound .. Elmt_High_Bound;
 484    --  Type used to identify an element list
 485
 486    No_Elmt : constant Elmt_Id := Elmt_Low_Bound;
 487    --  Used to represent empty element
 488
 489    First_Elmt_Id : constant Elmt_Id := No_Elmt + 1;
 490    --  Subscript of first allocated Elmt table entry
 491
 492    -------------------------------
 493    -- Types for Stringt Package --
 494    -------------------------------
 495
 496    --  String_Id values are used to identify entries in the strings table.
 497    --  They are subscripts into the strings table defined in package Strings.
 498
 499    --  Note that with only a few exceptions, which are clearly documented, the
 500    --  type String_Id should be regarded as a private type. In particular it is
 501    --  never appropriate to perform arithmetic operations using this type.
 502
 503    type String_Id is range Strings_Low_Bound .. Strings_High_Bound;
 504    --  Type used to identify entries in the strings table
 505
 506    No_String : constant String_Id := Strings_Low_Bound;
 507    --  Used to indicate missing string Id. Note that the value zero is used
 508    --  to indicate a missing data value for all the Int types in this section.
 509
 510    First_String_Id : constant String_Id := No_String + 1;
 511    --  First subscript allocated in string table
 512
 513    -------------------------
 514    -- Character Code Type --
 515    -------------------------
 516
 517    --  The type Char is used for character data internally in the compiler,
 518    --  but character codes in the source are represented by the Char_Code
 519    --  type. Each character literal in the source is interpreted as being one
 520    --  of the 2**16 possible Wide_Character codes, and a unique integer value
 521    --  is assigned, corresponding to the POS value in the Wide_Character type.
 522    --  String literals are similarly interpreted as a sequence of such codes.
 523
 524    --  Note: when character code values are stored in the tree, they are stored
 525    --  by adding a bias value (Char_Code_Bias) that results in values that can
 526    --  be distinguished from other types of values stored in the tree.
 527
 528    type Char_Code is mod 2 ** 16;
 529    for Char_Code'Size use 16;
 530
 531    function Get_Char_Code (C : Character) return Char_Code;
 532    pragma Inline (Get_Char_Code);
 533    --  Function to obtain internal character code from source character. For
 534    --  the moment, the internal character code is simply the Pos value of the
 535    --  input source character, but we provide this interface for possible
 536    --  later support of alternative character sets.
 537
 538    function In_Character_Range (C : Char_Code) return Boolean;
 539    pragma Inline (In_Character_Range);
 540    --  Determines if the given character code is in range of type Character,
 541    --  and if so, returns True. If not, returns False.
 542
 543    function Get_Character (C : Char_Code) return Character;
 544    pragma Inline (Get_Character);
 545    --  For a character C that is in character range (see above function), this
 546    --  function returns the corresponding Character value. It is an error to
 547    --  call Get_Character if C is not in character range
 548
 549    ---------------------------------------
 550    -- Types used for Library Management --
 551    ---------------------------------------
 552
 553    type Unit_Number_Type is new Int;
 554    --  Unit number. The main source is unit 0, and subsidiary sources have
 555    --  non-zero numbers starting with 1. Unit numbers are used to index the
 556    --  file table in Lib.
 557
 558    Main_Unit : constant Unit_Number_Type := 0;
 559    --  Unit number value for main unit
 560
 561    No_Unit : constant Unit_Number_Type := -1;
 562    --  Special value used to signal no unit
 563
 564    type Source_File_Index is new Nat;
 565    --  Type used to index the source file table (see package Sinput)
 566
 567    No_Source_File : constant Source_File_Index := 0;
 568    --  Value used to indicate no source file present
 569
 570    System_Source_File_Index : constant Source_File_Index := 1;
 571    --  Value used for source file table entry for system.ads, which is
 572    --  always the first source file read (see unit Targparm for details).
 573
 574    subtype File_Name_Type is Name_Id;
 575    --  File names are stored in the names table and this synonym is used to
 576    --  indicate that a Name_Id value is being used to hold a simple file
 577    --  name (which does not include any directory information).
 578
 579    No_File : constant File_Name_Type := File_Name_Type (No_Name);
 580    --  Constant used to indicate no file found
 581
 582    subtype Unit_Name_Type is Name_Id;
 583    --  Unit names are stored in the names table and this synonym is used to
 584    --  indicate that a Name_Id value is being used to hold a unit name.
 585
 586    -----------------------------------
 587    -- Representation of Time Stamps --
 588    -----------------------------------
 589
 590    --  All compiled units are marked with a time stamp which is derived from
 591    --  the source file (we assume that the host system has the concept of a
 592    --  file time stamp which is modified when a file is modified). These
 593    --  time stamps are used to ensure consistency of the set of units that
 594    --  constitutes a library. Time stamps are 12 character strings with
 595    --  with the following format:
 596
 597    --     YYYYMMDDHHMMSS
 598
 599    --       YYYY   year
 600    --       MM     month (2 digits 01-12)
 601    --       DD     day (2 digits 01-31)
 602    --       HH     hour (2 digits 00-23)
 603    --       MM     minutes (2 digits 00-59)
 604    --       SS     seconds (2 digits 00-59)
 605
 606    --  In the case of Unix systems (and other systems which keep the time in
 607    --  GMT), the time stamp is the GMT time of the file, not the local time.
 608    --  This solves problems in using libraries across networks with clients
 609    --  spread across multiple time-zones.
 610
 611    Time_Stamp_Length : constant := 14;
 612    --  Length of time stamp value
 613
 614    subtype Time_Stamp_Index is Natural range 1 .. Time_Stamp_Length;
 615    type Time_Stamp_Type is new String (Time_Stamp_Index);
 616    --  Type used to represent time stamp
 617
 618    Empty_Time_Stamp : constant Time_Stamp_Type := (others => ' ');
 619    --  Type used to represent an empty or missing time stamp. Looks less
 620    --  than any real time stamp if two time stamps are compared. Note that
 621    --  although this is not a private type, clients should not rely on the
 622    --  exact way in which this string is represented, and instead should
 623    --  use the subprograms below.
 624
 625    function "="  (Left, Right : Time_Stamp_Type) return Boolean;
 626    function "<=" (Left, Right : Time_Stamp_Type) return Boolean;
 627    function ">=" (Left, Right : Time_Stamp_Type) return Boolean;
 628    function "<"  (Left, Right : Time_Stamp_Type) return Boolean;
 629    function ">"  (Left, Right : Time_Stamp_Type) return Boolean;
 630    --  Comparison functions on time stamps. Note that two time stamps
 631    --  are defined as being equal if they have the same day/month/year
 632    --  and the hour/minutes/seconds values are within 2 seconds of one
 633    --  another. This deals with rounding effects in library file time
 634    --  stamps caused by copying operations during installation. We have
 635    --  particularly noticed that WinNT seems susceptible to such changes.
 636    --  Note: the Empty_Time_Stamp value looks equal to itself, and less
 637    --  than any non-empty time stamp value.
 638
 639    procedure Split_Time_Stamp
 640      (TS      : Time_Stamp_Type;
 641       Year    : out Nat;
 642       Month   : out Nat;
 643       Day     : out Nat;
 644       Hour    : out Nat;
 645       Minutes : out Nat;
 646       Seconds : out Nat);
 647    --  Given a time stamp, decompose it into its components
 648
 649    procedure Make_Time_Stamp
 650      (Year    : Nat;
 651       Month   : Nat;
 652       Day     : Nat;
 653       Hour    : Nat;
 654       Minutes : Nat;
 655       Seconds : Nat;
 656       TS      : out Time_Stamp_Type);
 657    --  Given the components of a time stamp, initialize the value
 658
 659    -----------------------------------------------
 660    -- Types used for Pragma Suppress Management --
 661    -----------------------------------------------
 662
 663    --  The following record contains an entry for each recognized check name
 664    --  for pragma Suppress. It is used to represent current settings of scope
 665    --  based suppress actions from pragma Suppress or command line settings.
 666
 667    type Suppress_Record is record
 668       Access_Checks        : Boolean;
 669       Accessibility_Checks : Boolean;
 670       Discriminant_Checks  : Boolean;
 671       Division_Checks      : Boolean;
 672       Elaboration_Checks   : Boolean;
 673       Index_Checks         : Boolean;
 674       Length_Checks        : Boolean;
 675       Overflow_Checks      : Boolean;
 676       Range_Checks         : Boolean;
 677       Storage_Checks       : Boolean;
 678       Tag_Checks           : Boolean;
 679    end record;
 680
 681    --  To add a new check type to GNAT, the following steps are required:
 682
 683    --    1.  Add an appropriate entry to the above record type
 684    --    2.  Add an entry to Snames spec and body for the new name
 685    --    3.  Add an entry to the definition of Check_Id in the Snames spec
 686    --    4.  Add a new entity flag definition in Einfo for the check
 687    --    5.  Add a new function to Sem.Util to handle the new check test
 688    --    6.  Add appropriate processing for pragma Suppress in Sem.Prag
 689    --    7.  Add a branch to the case statement in Sem.Ch8.Pop_Scope
 690    --    8.  Add a new Do_xxx_Check flag to Sinfo (if required)
 691    --    9.  Add appropriate checks for the new test
 692
 693    -----------------------------------
 694    -- Global Exception Declarations --
 695    -----------------------------------
 696
 697    --  This section contains declarations of exceptions that are used
 698    --  throughout the compiler.
 699
 700    Unrecoverable_Error : exception;
 701    --  This exception is raised to immediately terminate the compilation
 702    --  of the current source program. Used in situations where things are
 703    --  bad enough that it doesn't seem worth continuing (e.g. max errors
 704    --  reached, or a required file is not found). Also raised when the
 705    --  compiler finds itself in trouble after an error (see Comperr).
 706
 707    ---------------------------------
 708    -- Parameter Mechanism Control --
 709    ---------------------------------
 710
 711    --  Function and parameter entities have a field that records the
 712    --  passing mechanism. See specification of Sem_Mech for full details.
 713    --  The following subtype is used to represent values of this type:
 714
 715    subtype Mechanism_Type is Int range -10 .. Int'Last;
 716    --  Type used to represent a mechanism value. This is a subtype rather
 717    --  than a type to avoid some annoying processing problems with certain
 718    --  routines in Einfo (processing them to create the corresponding C).
 719
 720 end Types;