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 --                                                                          --
  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 -- As a special exception,  if other files  instantiate  generics from this --
  24 -- unit, or you link  this unit with other files  to produce an executable, --
  25 -- this  unit  does not  by itself cause  the resulting  executable  to  be --
  26 -- covered  by the  GNU  General  Public  License.  This exception does not --
  27 -- however invalidate  any other reasons why  the executable file  might be --
  28 -- covered by the  GNU Public License.                                      --
  29 --                                                                          --
  30 -- GNAT was originally developed  by the GNAT team at  New York University. --
  31 -- It is now maintained by Ada Core Technologies Inc (http://www.gnat.com). --
  32 --                                                                          --
  33 ------------------------------------------------------------------------------
  34
  35 with Unchecked_Deallocation;
  36
  37 package Types is
  38 pragma Preelaborate (Types);
  39
  40 --  This package contains host independent type definitions which are used
  41 --  in more than one unit in the compiler. They are gathered here for easy
  42 --  reference, though in some cases the full description is found in the
  43 --  relevant module which implements the definition. The main reason that
  44 --  they are not in their "natural" specs is that this would cause a lot of
  45 --  inter-spec dependencies, and in particular some awkward circular
  46 --  dependencies would have to be dealt with.
  47
  48 --  WARNING: There is a C version of this package. Any changes to this
  49 --  source file must be properly reflected in the C header file a-types.h
  50
  51 --  Note: the declarations in this package reflect an expectation that the
  52 --  host machine has an efficient integer base type with a range at least
  53 --  32 bits 2s-complement. If there are any machines for which this is not
  54 --  a correct assumption, a significant number of changes will be required!
  55
  56    -------------------------------
  57    -- General Use Integer Types --
  58    -------------------------------
  59
  60    type Int is range -2 ** 31 .. +2 ** 31 - 1;
  61    --  Signed 32-bit integer
  62
  63    type Dint is range -2 ** 63 .. +2 ** 63 - 1;
  64    --  Double length (64-bit) integer
  65
  66    subtype Nat is Int range 0 .. Int'Last;
  67    --  Non-negative Int values
  68
  69    subtype Pos is Int range 1 .. Int'Last;
  70    --  Positive Int values
  71
  72    type Word is mod 2 ** 32;
  73    --  Unsigned 32-bit integer
  74
  75    type Short is range -32768 .. +32767;
  76    for Short'Size use 16;
  77    --  16-bit signed integer
  78
  79    type Byte is mod 2 ** 8;
  80    for Byte'Size use 8;
  81    --  8-bit unsigned integer
  82
  83    type size_t is mod 2 ** Standard'Address_Size;
  84    --  Memory size value, for use in calls to C routines
  85
  86    --------------------------------------
  87    -- 8-Bit Character and String Types --
  88    --------------------------------------
  89
  90    --  We use Standard.Character and Standard.String freely, since we are
  91    --  compiling ourselves, and we properly implement the required 8-bit
  92    --  character code as required in Ada 95. This section defines a few
  93    --  general use constants and subtypes.
  94
  95    EOF : constant Character := ASCII.SUB;
  96    --  The character SUB (16#1A#) is used in DOS and other systems derived
  97    --  from DOS (OS/2, NT etc) to signal the end of a text file. Internally
  98    --  all source files are ended by an EOF character, even on Unix systems.
  99    --  An EOF character acts as the end of file only as the last character
 100    --  of a source buffer, in any other position, it is treated as a blank
 101    --  if it appears between tokens, and as an illegal character otherwise.
 102    --  This makes life easier dealing with files that originated from DOS,
 103    --  including concatenated files with interspersed EOF characters.
 104
 105    subtype Graphic_Character is Character range ' ' .. '~';
 106    --  Graphic characters, as defined in ARM
 107
 108    subtype Line_Terminator is Character range ASCII.LF .. ASCII.CR;
 109    --  Line terminator characters (LF, VT, FF, CR)
 110
 111    subtype Upper_Half_Character is
 112      Character range Character'Val (16#80#) .. Character'Val (16#FF#);
 113    --  Characters with the upper bit set
 114
 115    type Character_Ptr is access all Character;
 116    type String_Ptr    is access all String;
 117    --  Standard character and string pointers
 118
 119    procedure Free is new Unchecked_Deallocation (String, String_Ptr);
 120    --  Procedure for freeing dynamically allocated String values
 121
 122    subtype Word_Hex_String is String (1 .. 8);
 123    --  Type used to represent Word value as 8 hex digits, with lower case
 124    --  letters for the alphabetic cases.
 125
 126    function Get_Hex_String (W : Word) return Word_Hex_String;
 127    --  Convert word value to 8-character hex string
 128
 129    -----------------------------------------
 130    -- Types Used for Text Buffer Handling --
 131    -----------------------------------------
 132
 133    --  We can't use type String for text buffers, since we must use the
 134    --  standard 32-bit integer as an index value, since we count on all
 135    --  index values being the same size.
 136
 137    type Text_Ptr is new Int;
 138    --  Type used for subscripts in text buffer
 139
 140    type Text_Buffer is array (Text_Ptr range <>) of Character;
 141    --  Text buffer used to hold source file or library information file
 142
 143    type Text_Buffer_Ptr is access all Text_Buffer;
 144    --  Text buffers for input files are allocated dynamically and this type
 145    --  is used to reference these text buffers.
 146
 147    procedure Free is new Unchecked_Deallocation (Text_Buffer, Text_Buffer_Ptr);
 148    --  Procedure for freeing dynamically allocated text buffers
 149
 150    ------------------------------------------
 151    -- Types Used for Source Input Handling --
 152    ------------------------------------------
 153
 154    type Logical_Line_Number is range 0 .. Int'Last;
 155    for Logical_Line_Number'Size use 32;
 156    --  Line number type, used for storing logical line numbers (i.e. line
 157    --  numbers that include effects of any Source_Reference pragmas in the
 158    --  source file). The value zero indicates a line containing a source
 159    --  reference pragma.
 160
 161    No_Line_Number : constant Logical_Line_Number := 0;
 162    --  Special value used to indicate no line number
 163
 164    type Physical_Line_Number is range 1 .. Int'Last;
 165    for Physical_Line_Number'Size use 32;
 166    --  Line number type, used for storing physical line numbers (i.e.
 167    --  line numbers in the physical file being compiled, unaffected by
 168    --  the presence of source reference pragmas.
 169
 170    type Column_Number is range 0 .. 32767;
 171    for Column_Number'Size use 16;
 172    --  Column number (assume that 2**15 is large enough, see declaration
 173    --  of Hostparm.Max_Line_Length)
 174
 175    No_Column_Number : constant Column_Number := 0;
 176    --  Special value used to indicate no column number
 177
 178    subtype Source_Buffer is Text_Buffer;
 179    --  Type used to store text of a source file . The buffer for the main
 180    --  source (the source specified on the command line) has a lower bound
 181    --  starting at zero. Subsequent subsidiary sources have lower bounds
 182    --  which are one greater than the previous upper bound.
 183
 184    subtype Big_Source_Buffer is Text_Buffer (0 .. Text_Ptr'Last);
 185    --  This is a virtual type used as the designated type of the access
 186    --  type Source_Buffer_Ptr, see Osint.Read_Source_File for details.
 187
 188    type Source_Buffer_Ptr is access all Big_Source_Buffer;
 189    --  Pointer to source buffer. We use virtual origin addressing for
 190    --  source buffers, with thin pointers. The pointer points to a virtual
 191    --  instance of type Big_Source_Buffer, where the actual type is in fact
 192    --  of type Source_Buffer. The address is adjusted so that the virtual
 193    --  origin addressing works correctly. See Osint.Read_Source_Buffer for
 194    --  further details.
 195
 196    subtype Source_Ptr is Text_Ptr;
 197    --  Type used to represent a source location, which is a subscript of a
 198    --  character in the source buffer. As noted above, diffferent source
 199    --  buffers have different ranges, so it is possible to tell from a
 200    --  Source_Ptr value which source it refers to. Note that negative numbers
 201    --  are allowed to accommodate the following special values.
 202
 203    No_Location : constant Source_Ptr := -1;
 204    --  Value used to indicate no source position set in a node
 205
 206    Standard_Location : constant Source_Ptr := -2;
 207    --  Used for all nodes in the representation of package Standard other
 208    --  than nodes representing the contents of Standard.ASCII. Note that
 209    --  testing for <= Standard_Location tests for both Standard_Location
 210    --  and for Standard_ASCII_Location.
 211
 212    Standard_ASCII_Location : constant Source_Ptr := -3;
 213    --  Used for all nodes in the presentation of package Standard.ASCII
 214
 215    First_Source_Ptr : constant Source_Ptr := 0;
 216    --  Starting source pointer index value for first source program
 217
 218    -------------------------------------
 219    -- Range Definitions for Tree Data --
 220    -------------------------------------
 221
 222    --  The tree has fields that can hold any of the following types:
 223
 224    --    Pointers to other tree nodes (type Node_Id)
 225    --    List pointers (type List_Id)
 226    --    Element list pointers (type Elist_Id)
 227    --    Names (type Name_Id)
 228    --    Strings (type String_Id)
 229    --    Universal integers (type Uint)
 230    --    Universal reals (type Ureal)
 231    --    Character codes (type Char_Code stored with a bias)
 232
 233    --  In most contexts, the strongly typed interface determines which of
 234    --  these types is present. However, there are some situations (involving
 235    --  untyped traversals of the tree), where it is convenient to be easily
 236    --  able to distinguish these values. The underlying representation in all
 237    --  cases is an integer type Union_Id, and we ensure that the range of
 238    --  the various possible values for each of the above types is disjoint
 239    --  so that this distinction is possible.
 240
 241    type Union_Id is new Int;
 242    --  The type in the tree for a union of possible ID values
 243
 244    --  Note: it is also helpful for debugging purposes to make these ranges
 245    --  distinct. If a bug leads to misidentification of a value, then it will
 246    --  typically result in an out of range value and a Constraint_Error.
 247
 248    List_Low_Bound : constant := -100_000_000;
 249    --  The List_Id values are subscripts into an array of list headers which
 250    --  has List_Low_Bound as its lower bound. This value is chosen so that all
 251    --  List_Id values are negative, and the value zero is in the range of both
 252    --  List_Id and Node_Id values (see further description below).
 253
 254    List_High_Bound : constant := 0;
 255    --  Maximum List_Id subscript value. This allows up to 100 million list
 256    --  Id values, which is in practice infinite, and there is no need to
 257    --  check the range. The range overlaps the node range by one element
 258    --  (with value zero), which is used both for the Empty node, and for
 259    --  indicating no list. The fact that the same value is used is convenient
 260    --  because it means that the default value of Empty applies to both nodes
 261    --  and lists, and also is more efficient to test for.
 262
 263    Node_Low_Bound : constant := 0;
 264    --  The tree Id values start at zero, because we use zero for Empty (to
 265    --  allow a zero test for Empty). Actual tree node subscripts start at 0
 266    --  since Empty is a legitimate node value.
 267
 268    Node_High_Bound : constant := 099_999_999;
 269    --  Maximum number of nodes that can be allocated is 100 million, which
 270    --  is in practice infinite, and there is no need to check the range.
 271
 272    Elist_Low_Bound : constant := 100_000_000;
 273    --  The Elist_Id values are subscripts into an array of elist headers which
 274    --  has Elist_Low_Bound as its lower bound.
 275
 276    Elist_High_Bound : constant := 199_999_999;
 277    --  Maximum Elist_Id subscript value. This allows up to 100 million Elists,
 278    --  which is in practice infinite and there is no need to check the range.
 279
 280    Elmt_Low_Bound : constant := 200_000_000;
 281    --  Low bound of element Id values. The use of these values is internal to
 282    --  the Elists package, but the definition of the range is included here
 283    --  since it must be disjoint from other Id values. The Elmt_Id values are
 284    --  subscripts into an array of list elements which has this as lower bound.
 285
 286    Elmt_High_Bound : constant := 299_999_999;
 287    --  Upper bound of Elmt_Id values. This allows up to 100 million element
 288    --  list members, which is in practice infinite (no range check needed).
 289
 290    Names_Low_Bound : constant := 300_000_000;
 291    --  Low bound for name Id values
 292
 293    Names_High_Bound : constant := 399_999_999;
 294    --  Maximum number of names that can be allocated is 100 million, which is
 295    --  in practice infinite and there is no need to check the range.
 296
 297    Strings_Low_Bound : constant := 400_000_000;
 298    --  Low bound for string Id values
 299
 300    Strings_High_Bound : constant := 499_999_999;
 301    --  Maximum number of strings that can be allocated is 100 million, which
 302    --  is in practice infinite and there is no need to check the range.
 303
 304    Ureal_Low_Bound : constant := 500_000_000;
 305    --  Low bound for Ureal values.
 306
 307    Ureal_High_Bound : constant := 599_999_999;
 308    --  Maximum number of Ureal values stored is 100_000_000 which is in
 309    --  practice infinite so that no check is required.
 310
 311    Uint_Low_Bound : constant := 600_000_000;
 312    --  Low bound for Uint values.
 313
 314    Uint_Table_Start : constant := 2_000_000_000;
 315    --  Location where table entries for universal integers start (see
 316    --  Uintp spec for details of the representation of Uint values).
 317
 318    Uint_High_Bound : constant := 2_099_999_999;
 319    --  The range of Uint values is very large, since a substantial part
 320    --  of this range is used to store direct values, see Uintp for details.
 321
 322    Char_Code_Bias : constant := 2_100_000_000;
 323    --  A bias value added to character code values stored in the tree which
 324    --  ensures that they have different values from any of the above types.
 325
 326    --  The following subtype definitions are used to provide convenient names
 327    --  for membership tests on Int values to see what data type range they
 328    --  lie in. Such tests appear only in the lowest level packages.
 329
 330    subtype List_Range      is Union_Id
 331      range List_Low_Bound   .. List_High_Bound;
 332
 333    subtype Node_Range      is Union_Id
 334      range Node_Low_Bound   .. Node_High_Bound;
 335
 336    subtype Elist_Range     is Union_Id
 337      range Elist_Low_Bound  .. Elist_High_Bound;
 338
 339    subtype Elmt_Range      is Union_Id
 340      range Elmt_Low_Bound   .. Elmt_High_Bound;
 341
 342    subtype Names_Range     is Union_Id
 343      range Names_Low_Bound   .. Names_High_Bound;
 344
 345    subtype Strings_Range   is Union_Id
 346      range Strings_Low_Bound .. Strings_High_Bound;
 347
 348    subtype Uint_Range      is Union_Id
 349      range Uint_Low_Bound    .. Uint_High_Bound;
 350
 351    subtype Ureal_Range     is Union_Id
 352      range Ureal_Low_Bound    .. Ureal_High_Bound;
 353
 354    subtype Char_Code_Range is Union_Id
 355      range Char_Code_Bias    .. Char_Code_Bias + 2**16 - 1;
 356
 357    -----------------------------
 358    -- Types for Namet Package --
 359    -----------------------------
 360
 361    --  Name_Id values are used to identify entries in the names table. Except
 362    --  for the special values No_Name, and Error_Name, they are subscript
 363    --  values for the Names table defined in package Namet.
 364
 365    --  Note that with only a few exceptions, which are clearly documented, the
 366    --  type Name_Id should be regarded as a private type. In particular it is
 367    --  never appropriate to perform arithmetic operations using this type.
 368
 369    type Name_Id is range Names_Low_Bound .. Names_High_Bound;
 370    for Name_Id'Size use 32;
 371    --  Type used to identify entries in the names table
 372
 373    No_Name : constant Name_Id := Names_Low_Bound;
 374    --  The special Name_Id value No_Name is used in the parser to indicate
 375    --  a situation where no name is present (e.g. on a loop or block).
 376
 377    Error_Name : constant Name_Id := Names_Low_Bound +  1;
 378    --  The special Name_Id value Error_Name is used in the parser to
 379    --  indicate that some kind of error was encountered in scanning out
 380    --  the relevant name, so it does not have a representable label.
 381
 382    subtype Error_Name_Or_No_Name is Name_Id range No_Name .. Error_Name;
 383    --  Used to test for either error name or no name
 384
 385    First_Name_Id : constant Name_Id := Names_Low_Bound + 2;
 386    --  Subscript of first entry in names table
 387
 388    ----------------------------
 389    -- Types for Atree Package --
 390    ----------------------------
 391
 392    --  Node_Id values are used to identify nodes in the tree. They are
 393    --  subscripts into the Node table declared in package Tree. Note that
 394    --  the special values Empty and Error are subscripts into this table,
 395    --  See package Atree for further details.
 396
 397    type Node_Id is range Node_Low_Bound .. Node_High_Bound;
 398    --  Type used to identify nodes in the tree
 399
 400    subtype Entity_Id is Node_Id;
 401    --  A synonym for node types, used in the entity package to refer to
 402    --  nodes that are entities (i.e. nodes with an Nkind of N_Defining_xxx)
 403    --  All such nodes are extended nodes and these are the only extended
 404    --  nodes, so that in practice entity and extended nodes are synonymous.
 405
 406    subtype Node_Or_Entity_Id is Node_Id;
 407    --  A synonym for node types, used in cases where a given value may be used
 408    --  to represent either a node or an entity. We like to minimize such uses
 409    --  for obvious reasons of logical type consistency, but where such uses
 410    --  occur, they should be documented by use of this type.
 411
 412    Empty : constant Node_Id := Node_Low_Bound;
 413    --  Used to indicate null node. A node is actually allocated with this
 414    --  Id value, so that Nkind (Empty) = N_Empty. Note that Node_Low_Bound
 415    --  is zero, so Empty = No_List = zero.
 416
 417    Empty_List_Or_Node : constant := 0;
 418    --  This constant is used in situations (e.g. initializing empty fields)
 419    --  where the value set will be used to represent either an empty node
 420    --  or a non-existent list, depending on the context.
 421
 422    Error : constant Node_Id := Node_Low_Bound + 1;
 423    --  Used to indicate that there was an error in the source program. A node
 424    --  is actually allocated at this address, so that Nkind (Error) = N_Error.
 425
 426    Empty_Or_Error : constant Node_Id := Error;
 427    --  Since Empty and Error are the first two Node_Id values, the test for
 428    --  N <= Empty_Or_Error tests to see if N is Empty or Error. This definition
 429    --  provides convenient self-documentation for such tests.
 430
 431    First_Node_Id  : constant Node_Id := Node_Low_Bound;
 432    --  Subscript of first allocated node. Note that Empty and Error are both
 433    --  allocated nodes, whose Nkind fields can be accessed without error.
 434
 435    ------------------------------
 436    -- Types for Nlists Package --
 437    ------------------------------
 438
 439    --  List_Id values are used to identify node lists in the tree. They are
 440    --  subscripts into the Lists table declared in package Tree. Note that
 441    --  the special value Error_List is a subscript in this table, but the
 442    --  value No_List is *not* a valid subscript, and any attempt to apply
 443    --  list operations to No_List will cause a (detected) error.
 444
 445    type List_Id is range List_Low_Bound .. List_High_Bound;
 446    --  Type used to identify a node list
 447
 448    No_List : constant List_Id := List_High_Bound;
 449    --  Used to indicate absence of a list. Note that the value is zero, which
 450    --  is the same as Empty, which is helpful in initializing nodes where a
 451    --  value of zero can represent either an empty node or an empty list.
 452
 453    Error_List : constant List_Id := List_Low_Bound;
 454    --  Used to indicate that there was an error in the source program in a
 455    --  context which would normally require a list. This node appears to be
 456    --  an empty list to the list operations (a null list is actually allocated
 457    --  which has this Id value).
 458
 459    First_List_Id : constant List_Id := Error_List;
 460    --  Subscript of first allocated list header
 461
 462    ------------------------------
 463    -- Types for Elists Package --
 464    ------------------------------
 465
 466    --  Element list Id values are used to identify element lists stored in
 467    --  the tree (see package Tree for further details). They are formed by
 468    --  adding a bias (Element_List_Bias) to subscript values in the same
 469    --  array that is used for node list headers.
 470
 471    type Elist_Id is range Elist_Low_Bound .. Elist_High_Bound;
 472    --  Type used to identify an element list (Elist header table subscript)
 473
 474    No_Elist : constant Elist_Id := Elist_Low_Bound;
 475    --  Used to indicate absense of an element list. Note that this is not
 476    --  an actual Elist header, so element list operations on this value
 477    --  are not valid.
 478
 479    First_Elist_Id : constant Elist_Id := No_Elist + 1;
 480    --  Subscript of first allocated Elist header.
 481
 482    --  Element Id values are used to identify individual elements of an
 483    --  element list (see package Elists for further details).
 484
 485    type Elmt_Id is range Elmt_Low_Bound .. Elmt_High_Bound;
 486    --  Type used to identify an element list
 487
 488    No_Elmt : constant Elmt_Id := Elmt_Low_Bound;
 489    --  Used to represent empty element
 490
 491    First_Elmt_Id : constant Elmt_Id := No_Elmt + 1;
 492    --  Subscript of first allocated Elmt table entry
 493
 494    -------------------------------
 495    -- Types for Stringt Package --
 496    -------------------------------
 497
 498    --  String_Id values are used to identify entries in the strings table.
 499    --  They are subscripts into the strings table defined in package Strings.
 500
 501    --  Note that with only a few exceptions, which are clearly documented, the
 502    --  type String_Id should be regarded as a private type. In particular it is
 503    --  never appropriate to perform arithmetic operations using this type.
 504
 505    type String_Id is range Strings_Low_Bound .. Strings_High_Bound;
 506    --  Type used to identify entries in the strings table
 507
 508    No_String : constant String_Id := Strings_Low_Bound;
 509    --  Used to indicate missing string Id. Note that the value zero is used
 510    --  to indicate a missing data value for all the Int types in this section.
 511
 512    First_String_Id : constant String_Id := No_String + 1;
 513    --  First subscript allocated in string table
 514
 515    -------------------------
 516    -- Character Code Type --
 517    -------------------------
 518
 519    --  The type Char is used for character data internally in the compiler,
 520    --  but character codes in the source are represented by the Char_Code
 521    --  type. Each character literal in the source is interpreted as being one
 522    --  of the 2**16 possible Wide_Character codes, and a unique integer value
 523    --  is assigned, corresponding to the POS value in the Wide_Character type.
 524    --  String literals are similarly interpreted as a sequence of such codes.
 525
 526    --  Note: when character code values are stored in the tree, they are stored
 527    --  by adding a bias value (Char_Code_Bias) that results in values that can
 528    --  be distinguished from other types of values stored in the tree.
 529
 530    type Char_Code is mod 2 ** 16;
 531    for Char_Code'Size use 16;
 532
 533    function Get_Char_Code (C : Character) return Char_Code;
 534    pragma Inline (Get_Char_Code);
 535    --  Function to obtain internal character code from source character. For
 536    --  the moment, the internal character code is simply the Pos value of the
 537    --  input source character, but we provide this interface for possible
 538    --  later support of alternative character sets.
 539
 540    function In_Character_Range (C : Char_Code) return Boolean;
 541    pragma Inline (In_Character_Range);
 542    --  Determines if the given character code is in range of type Character,
 543    --  and if so, returns True. If not, returns False.
 544
 545    function Get_Character (C : Char_Code) return Character;
 546    pragma Inline (Get_Character);
 547    --  For a character C that is in character range (see above function), this
 548    --  function returns the corresponding Character value. It is an error to
 549    --  call Get_Character if C is not in character range
 550
 551    ---------------------------------------
 552    -- Types used for Library Management --
 553    ---------------------------------------
 554
 555    type Unit_Number_Type is new Int;
 556    --  Unit number. The main source is unit 0, and subsidiary sources have
 557    --  non-zero numbers starting with 1. Unit numbers are used to index the
 558    --  file table in Lib.
 559
 560    Main_Unit : constant Unit_Number_Type := 0;
 561    --  Unit number value for main unit
 562
 563    No_Unit : constant Unit_Number_Type := -1;
 564    --  Special value used to signal no unit
 565
 566    type Source_File_Index is new Nat;
 567    --  Type used to index the source file table (see package Sinput)
 568
 569    No_Source_File : constant Source_File_Index := 0;
 570    --  Value used to indicate no source file present
 571
 572    System_Source_File_Index : constant Source_File_Index := 1;
 573    --  Value used for source file table entry for system.ads, which is
 574    --  always the first source file read (see unit Targparm for details).
 575
 576    subtype File_Name_Type is Name_Id;
 577    --  File names are stored in the names table and this synonym is used to
 578    --  indicate that a Name_Id value is being used to hold a simple file
 579    --  name (which does not include any directory information).
 580
 581    No_File : constant File_Name_Type := File_Name_Type (No_Name);
 582    --  Constant used to indicate no file found
 583
 584    subtype Unit_Name_Type is Name_Id;
 585    --  Unit names are stored in the names table and this synonym is used to
 586    --  indicate that a Name_Id value is being used to hold a unit name.
 587
 588    -----------------------------------
 589    -- Representation of Time Stamps --
 590    -----------------------------------
 591
 592    --  All compiled units are marked with a time stamp which is derived from
 593    --  the source file (we assume that the host system has the concept of a
 594    --  file time stamp which is modified when a file is modified). These
 595    --  time stamps are used to ensure consistency of the set of units that
 596    --  constitutes a library. Time stamps are 12 character strings with
 597    --  with the following format:
 598
 599    --     YYYYMMDDHHMMSS
 600
 601    --       YYYY   year
 602    --       MM     month (2 digits 01-12)
 603    --       DD     day (2 digits 01-31)
 604    --       HH     hour (2 digits 00-23)
 605    --       MM     minutes (2 digits 00-59)
 606    --       SS     seconds (2 digits 00-59)
 607
 608    --  In the case of Unix systems (and other systems which keep the time in
 609    --  GMT), the time stamp is the GMT time of the file, not the local time.
 610    --  This solves problems in using libraries across networks with clients
 611    --  spread across multiple time-zones.
 612
 613    Time_Stamp_Length : constant := 14;
 614    --  Length of time stamp value
 615
 616    subtype Time_Stamp_Index is Natural range 1 .. Time_Stamp_Length;
 617    type Time_Stamp_Type is new String (Time_Stamp_Index);
 618    --  Type used to represent time stamp
 619
 620    Empty_Time_Stamp : constant Time_Stamp_Type := (others => ' ');
 621    --  Type used to represent an empty or missing time stamp. Looks less
 622    --  than any real time stamp if two time stamps are compared. Note that
 623    --  although this is not a private type, clients should not rely on the
 624    --  exact way in which this string is represented, and instead should
 625    --  use the subprograms below.
 626
 627    Dummy_Time_Stamp : constant Time_Stamp_Type := (others => '0');
 628    --  This is used for dummy time stamp values used in the D lines for
 629    --  non-existant files, and is intended to be an impossible value.
 630
 631    function "="  (Left, Right : Time_Stamp_Type) return Boolean;
 632    function "<=" (Left, Right : Time_Stamp_Type) return Boolean;
 633    function ">=" (Left, Right : Time_Stamp_Type) return Boolean;
 634    function "<"  (Left, Right : Time_Stamp_Type) return Boolean;
 635    function ">"  (Left, Right : Time_Stamp_Type) return Boolean;
 636    --  Comparison functions on time stamps. Note that two time stamps
 637    --  are defined as being equal if they have the same day/month/year
 638    --  and the hour/minutes/seconds values are within 2 seconds of one
 639    --  another. This deals with rounding effects in library file time
 640    --  stamps caused by copying operations during installation. We have
 641    --  particularly noticed that WinNT seems susceptible to such changes.
 642    --  Note: the Empty_Time_Stamp value looks equal to itself, and less
 643    --  than any non-empty time stamp value.
 644
 645    procedure Split_Time_Stamp
 646      (TS      : Time_Stamp_Type;
 647       Year    : out Nat;
 648       Month   : out Nat;
 649       Day     : out Nat;
 650       Hour    : out Nat;
 651       Minutes : out Nat;
 652       Seconds : out Nat);
 653    --  Given a time stamp, decompose it into its components
 654
 655    procedure Make_Time_Stamp
 656      (Year    : Nat;
 657       Month   : Nat;
 658       Day     : Nat;
 659       Hour    : Nat;
 660       Minutes : Nat;
 661       Seconds : Nat;
 662       TS      : out Time_Stamp_Type);
 663    --  Given the components of a time stamp, initialize the value
 664
 665    -----------------------------------------------
 666    -- Types used for Pragma Suppress Management --
 667    -----------------------------------------------
 668
 669    --  The following record contains an entry for each recognized check name
 670    --  for pragma Suppress. It is used to represent current settings of scope
 671    --  based suppress actions from pragma Suppress or command line settings.
 672
 673    type Suppress_Record is record
 674       Access_Checks        : Boolean;
 675       Accessibility_Checks : Boolean;
 676       Discriminant_Checks  : Boolean;
 677       Division_Checks      : Boolean;
 678       Elaboration_Checks   : Boolean;
 679       Index_Checks         : Boolean;
 680       Length_Checks        : Boolean;
 681       Overflow_Checks      : Boolean;
 682       Range_Checks         : Boolean;
 683       Storage_Checks       : Boolean;
 684       Tag_Checks           : Boolean;
 685    end record;
 686
 687    --  To add a new check type to GNAT, the following steps are required:
 688
 689    --    1.  Add an appropriate entry to the above record type
 690    --    2.  Add an entry to Snames spec and body for the new name
 691    --    3.  Add an entry to the definition of Check_Id in the Snames spec
 692    --    4.  Add a new entity flag definition in Einfo for the check
 693    --    5.  Add a new function to Sem.Util to handle the new check test
 694    --    6.  Add appropriate processing for pragma Suppress in Sem.Prag
 695    --    7.  Add a branch to the case statement in Sem.Ch8.Pop_Scope
 696    --    8.  Add a new Do_xxx_Check flag to Sinfo (if required)
 697    --    9.  Add appropriate checks for the new test
 698
 699    -----------------------------------
 700    -- Global Exception Declarations --
 701    -----------------------------------
 702
 703    --  This section contains declarations of exceptions that are used
 704    --  throughout the compiler.
 705
 706    Unrecoverable_Error : exception;
 707    --  This exception is raised to immediately terminate the compilation
 708    --  of the current source program. Used in situations where things are
 709    --  bad enough that it doesn't seem worth continuing (e.g. max errors
 710    --  reached, or a required file is not found). Also raised when the
 711    --  compiler finds itself in trouble after an error (see Comperr).
 712
 713    ---------------------------------
 714    -- Parameter Mechanism Control --
 715    ---------------------------------
 716
 717    --  Function and parameter entities have a field that records the
 718    --  passing mechanism. See specification of Sem_Mech for full details.
 719    --  The following subtype is used to represent values of this type:
 720
 721    subtype Mechanism_Type is Int range -10 .. Int'Last;
 722    --  Type used to represent a mechanism value. This is a subtype rather
 723    --  than a type to avoid some annoying processing problems with certain
 724    --  routines in Einfo (processing them to create the corresponding C).
 725
 726    ------------------------------
 727    -- Run-Time Exception Codes --
 728    ------------------------------
 729
 730    --  When the code generator generates a run-time exception, it provides
 731    --  a reason code which is one of the following. This reason code is used
 732    --  to select the appropriate run-time routine to be called, determining
 733    --  both the exception to be raised, and the message text to be added.
 734
 735    --  The prefix CE/PE/SE indicates the exception to be raised
 736    --    CE = Constraint_Error
 737    --    PE = Program_Error
 738    --    SE = Storage_Error
 739
 740    --  The remaining part of the name indicates the message text to be added,
 741    --  where all letters are lower case, and underscores are converted to
 742    --  spaces (for example CE_Invalid_Data adds the text "invalid data").
 743
 744    --  To add a new code, you need to do the following:
 745
 746    --    1. Modify the type and subtype declarations below appropriately,
 747    --       keeping things in alphabetical order.
 748
 749    --    2. Modify the corresponding definitions in a-types.h, including
 750    --       the definition of last_reason_code.
 751
 752    --    3. Add a new routine in Ada.Exceptions with the appropriate call
 753    --       and static string constant
 754
 755    --    4. Initialize the new entry in raise_decls
 756
 757    type RT_Exception_Code is (
 758      CE_Access_Check_Failed,
 759      CE_Access_Parameter_Is_Null,
 760      CE_Discriminant_Check_Failed,
 761      CE_Divide_By_Zero,
 762      CE_Explicit_Raise,
 763      CE_Index_Check_Failed,
 764      CE_Invalid_Data,
 765      CE_Length_Check_Failed,
 766      CE_Overflow_Check_Failed,
 767      CE_Partition_Check_Failed,
 768      CE_Range_Check_Failed,
 769      CE_Tag_Check_Failed,
 770
 771      PE_Access_Before_Elaboration,
 772      PE_Accessibility_Check_Failed,
 773      PE_All_Guards_Closed,
 774      PE_Duplicated_Entry_Address,
 775      PE_Explicit_Raise,
 776      PE_Finalize_Raised_Exception,
 777      PE_Invalid_Data,
 778      PE_Misaligned_Address_Value,
 779      PE_Missing_Return,
 780      PE_Potentially_Blocking_Operation,
 781      PE_Stubbed_Subprogram_Called,
 782      PE_Unchecked_Union_Restriction,
 783
 784      SE_Empty_Storage_Pool,
 785      SE_Explicit_Raise,
 786      SE_Infinite_Recursion,
 787      SE_Object_Too_Large,
 788      SE_Restriction_Violation);
 789
 790    subtype RT_CE_Exceptions is RT_Exception_Code range
 791      CE_Access_Check_Failed ..
 792      CE_Tag_Check_Failed;
 793
 794    subtype RT_PE_Exceptions is RT_Exception_Code range
 795      PE_Access_Before_Elaboration ..
 796      PE_Unchecked_Union_Restriction;
 797
 798    subtype RT_SE_Exceptions is RT_Exception_Code range
 799      SE_Empty_Storage_Pool ..
 800      SE_Restriction_Violation;
 801
 802 end Types;