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File : system.ads


------------------------------------------------------------------------------
--                                                                          --
--                        GNAT RUN-TIME COMPONENTS                          --
--                                                                          --
--                               S Y S T E M                                --
--                                                                          --
--                                 S p e c                                  --
--                               (NT Version)                               --
--                                                                          --
--                            $Revision: 1.8 $
--                                                                          --
--          Copyright (C) 1992-1999 Free Software Foundation, Inc.          --
--                                                                          --
-- This specification is derived from the Ada Reference Manual for use with --
-- GNAT. The copyright notice above, and the license provisions that follow --
-- apply solely to the  contents of the part following the private keyword. --
--                                                                          --
-- GNAT is free software;  you can  redistribute it  and/or modify it under --
-- terms of the  GNU General Public License as published  by the Free Soft- --
-- ware  Foundation;  either version 2,  or (at your option) any later ver- --
-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
-- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
-- for  more details.  You should have  received  a copy of the GNU General --
-- Public License  distributed with GNAT;  see file COPYING.  If not, write --
-- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
-- MA 02111-1307, USA.                                                      --
--                                                                          --
-- As a special exception,  if other files  instantiate  generics from this --
-- unit, or you link  this unit with other files  to produce an executable, --
-- this  unit  does not  by itself cause  the resulting  executable  to  be --
-- covered  by the  GNU  General  Public  License.  This exception does not --
-- however invalidate  any other reasons why  the executable file  might be --
-- covered by the  GNU Public License.                                      --
--                                                                          --
-- GNAT was originally developed  by the GNAT team at  New York University. --
-- It is now maintained by Ada Core Technologies Inc (http://www.gnat.com). --
--                                                                          --
------------------------------------------------------------------------------

package System is
pragma Pure (System);
--  Note that we take advantage of the implementation permission to
--  make this unit Pure instead of Preelaborable, see RM 13.7(36)

   type Name is (SYSTEM_NAME_GNAT);
   System_Name : constant Name := SYSTEM_NAME_GNAT;

   --  System-Dependent Named Numbers

   Min_Int               : constant := Long_Long_Integer'First;
   Max_Int               : constant := Long_Long_Integer'Last;

   Max_Binary_Modulus    : constant := 2 ** Long_Long_Integer'Size;
   Max_Nonbinary_Modulus : constant := Integer'Last;

   Max_Base_Digits       : constant := Long_Long_Float'Digits;
   Max_Digits            : constant := Long_Long_Float'Digits;

   Max_Mantissa          : constant := 63;
   Fine_Delta            : constant := 2.0 ** (-Max_Mantissa);

   Tick                  : constant := Standard'Tick;

   --  Storage-related Declarations

   type Address is private;
   Null_Address : constant Address;

   Storage_Unit : constant := Standard'Storage_Unit;
   Word_Size    : constant := Standard'Word_Size;
   Memory_Size  : constant := 2 ** Standard'Address_Size;

   --  Address comparison

   function "<"  (Left, Right : Address) return Boolean;
   function "<=" (Left, Right : Address) return Boolean;
   function ">"  (Left, Right : Address) return Boolean;
   function ">=" (Left, Right : Address) return Boolean;
   function "="  (Left, Right : Address) return Boolean;

   pragma Import (Intrinsic, "<");
   pragma Import (Intrinsic, "<=");
   pragma Import (Intrinsic, ">");
   pragma Import (Intrinsic, ">=");
   pragma Import (Intrinsic, "=");

   --  Other System-Dependent Declarations

   type Bit_Order is (High_Order_First, Low_Order_First);
   Default_Bit_Order : constant Bit_Order;

   --  Priority-related Declarations (RM D.1)

   subtype Any_Priority is Integer
     range 0 .. Standard'Max_Interrupt_Priority;

   subtype Priority is Any_Priority
     range 0 .. Standard'Max_Priority;

   --  Functional notation is needed in the following to avoid visibility
   --  problems when this package is compiled through rtsfind in the middle
   --  of another compilation.

   subtype Interrupt_Priority is Any_Priority
     range
       Standard."+" (Standard'Max_Priority,  1) ..
         Standard'Max_Interrupt_Priority;

   Default_Priority : constant Priority :=
     Standard."/" (Standard."+" (Priority'First, Priority'Last), 2);

private

   type Address is mod Memory_Size;
   Null_Address : constant Address := 0;

   Default_Bit_Order : constant Bit_Order :=
                         Bit_Order'Val (Standard'Default_Bit_Order);

   --------------------------------------
   -- System Implementation Parameters --
   --------------------------------------

   --  These parameters provide information about the target that is used
   --  by the compiler. They are in the private part of System, where they
   --  can be accessed using Rtsfind. All values defined here must be
   --  constants, since they are accessed at compile time.

   --  Note these definitions must come before the definitions of any
   --  complex types or other code that may require Rtsfind to access
   --  these entities during compilation of System itself.

   -----------------------------------
   -- Control of Exception Handling --
   -----------------------------------

   --  GNAT provides two methods of implementing exceptions:

   --    Longjmp/Setjmp (-gnatL)

   --      This approach uses longjmp/setjmp to handle exceptions. It
   --      uses less storage, and can often propagate exceptions faster,
   --      at the expense of (sometimes considerable) overhead in setting
   --      up an exception handler. This approach is available on all
   --      targets, and is the default where it is the only approach.

   --    Zero Cost (-gnatZ)

   --      This approach uses separate exception tables. These use extra
   --      storage, and exception propagation can be quite slow, but there
   --      is no overhead in setting up an exception handler (it is to this
   --      latter operation that the phrase zero-cost refers). This approach
   --      is only available on some targets, and is the default where it is
   --      available.

   Zero_Cost_Exceptions : constant Boolean := False;
   --  Set False for Longjmp/Setjmp, True for Zero Cost

   -------------------------------
   -- Control of Stack Checking --
   -------------------------------

   --  GNAT provides two methods of implementing exceptions:

   --    GCC Probing Mechanism

   --      This approach uses the standard GCC mechanism for
   --      stack checking. The method assumes that accessing
   --      storage immediately beyond the end of the stack
   --      will result in a trap that is converted to a storage
   --      error by the runtime system. This mechanism has
   --      minimal overhead, but requires complex hardware,
   --      operating system and run-time support. Probing is
   --      the default method where it is available. The stack
   --      size for the environment task depends on the operating
   --      system and cannot be set in a system-independent way.

   --   GNAT Stack-limit Checking

   --      This method relies on comparing the stack pointer
   --      with per-task stack limits. If the check fails, an
   --      exception is explicitly raised. The advantage is
   --      that the method requires no extra system dependent
   --      runtime support and can be used on systems without
   --      memory protection as well, but at the cost of more
   --      overhead for doing the check. This method is the
   --      default on systems that lack complete support for
   --      probing. The stack size for the environment task is

   Stack_Check_Probes : constant Boolean := False;
   --  Set True for GCC Probing, False for GNAT Stack-limit Checking

   Stack_Check_Default : constant Boolean := False;
   --  Set True for systems where stack checking is performed by default

   ---------------------------
   -- Underlying Priorities --
   ---------------------------

   --  Important note: this section of the file must come AFTER the
   --  definition of the system implementation parameters to ensure
   --  that the value of these parameters is available for analysis
   --  of the declarations here (using Rtsfind at compile time).

   --  The underlying priorities table provides a generalized mechanism
   --  for mapping from Ada priorities to system priorities. In some
   --  cases a 1-1 mapping is not the convenient or optimal choice.

   type Priorities_Mapping is array (Any_Priority) of Integer;
   pragma Suppress_Initialization (Priorities_Mapping);
   --  Suppress initialization in case gnat.adc specifies Normalize_Scalars

   --  On NT, the default mapping preserves the standard 31 priorities
   --  of the Ada model, but maps them using compression onto the 7
   --  priority levels available in NT.

   --  To replace the default values of the Underlying_Priorities mapping,
   --  copy this source file into your build directory, edit the file to
   --  reflect your desired behavior, and recompile with the command:

   --     $ gcc -c -O3 -gnatpgn system.ads

   --  then recompile the run-time parts that depend on this package:

   --     $ gnatmake -a -gnatn -O3 <your application>

   --  then force rebuilding your application if you need different options:

   --     $ gnatmake -f <your options> <your application>


   Underlying_Priorities : constant Priorities_Mapping :=

     (Priority'First .. 1        => -15,

      2 .. Default_Priority - 2  => -2,

      Default_Priority - 1       => -1,

      Default_Priority           => 0,

      Default_Priority + 1 .. 19 => 1,

      20 .. Priority'Last        => 2,

      Interrupt_Priority         => 15);

end System;