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13.7 The Package System

For each implementation there is a library package called System which includes the definitions of certain configuration-dependent characteristics.

Static Semantics

The following language-defined library package exists:

   
       package System is
          pragma Preelaborate(System);

          type Name is implementation-defined-enumeration-type;
          System_Name : constant Name := implementation-defined;

          -- System-Dependent Named Numbers:

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


          Max_Binary_Modulus    : constant := implementation-defined;
          Max_Nonbinary_Modulus : constant := implementation-defined;


          Max_Base_Digits       : constant := root_real'Digits;
          Max_Digits            : constant := implementation-defined;


          Max_Mantissa          : constant := implementation-defined;
          Fine_Delta            : constant := implementation-defined;


          Tick                  : constant := implementation-defined;


          -- Storage-related Declarations:

          type Address is implementation-defined;
          Null_Address : constant Address;


          Storage_Unit : constant := implementation-defined;
          Word_Size    : constant := implementation-defined * Storage_Unit;
          Memory_Size  : constant := implementation-defined;


          -- 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;
       -- function "/=" (Left, Right : Address) return Boolean;
          -- "/=" is implicitly defined
          pragma Convention(Intrinsic, "<");
          ... -- and so on for all language-defined subprograms in this package

          -- Other System-Dependent Declarations:
          type Bit_Order is (High_Order_First, Low_Order_First);
          Default_Bit_Order : constant Bit_Order;

          -- Priority-related declarations (see D.1):
          subtype Any_Priority is Integer range implementation-defined;
          subtype Priority is Any_Priority range Any_Priority'First .. implementation-defined;
          subtype Interrupt_Priority is Any_Priority range Priority'Last+1 .. Any_Priority'Last;

          Default_Priority : constant Priority := (Priority'First + Priority'Last)/2;

       private
          ... -- not specified by the language
       end System;

Name is an enumeration subtype. Values of type Name are the names of alternative machine configurations handled by the implementation. System_Name represents the current machine configuration.

The named numbers Fine_Delta and Tick are of the type universal_real; the others are of the type universal_integer.

The meanings of the named numbers are:

Min_Int

The smallest (most negative) value allowed for the expressions of a signed_integer_type_definition.

Max_Int

The largest (most positive) value allowed for the expressions of a signed_integer_type_definition.

Max_Binary_Modulus

A power of two such that it, and all lesser positive powers of two, are allowed as the modulus of a modular_type_definition.

Max_Nonbinary_Modulus

A value such that it, and all lesser positive integers, are allowed as the modulus of a modular_type_definition.

Max_Base_Digits

The largest value allowed for the requested decimal precision in a floating_point_definition.

Max_Digits

The largest value allowed for the requested decimal precision in a floating_point_definition that has no real_range_specification. Max_Digits is less than or equal to Max_Base_Digits.

Max_Mantissa

The largest possible number of binary digits in the mantissa of machine numbers of a user-defined ordinary fixed point type. (The mantissa is defined in Annex G.)

Fine_Delta

The smallest delta allowed in an ordinary_fixed_point_definition that has the real_range_specification range -1.0 .. 1.0.

Tick

A period in seconds approximating the real time interval during which the value of Calendar.Clock remains constant.

Storage_Unit

The number of bits per storage element.

Word_Size

The number of bits per word.

Memory_Size

An implementation-defined value that is intended to reflect the memory size of the configuration in storage elements.

Address is of a definite, nonlimited type. Address represents machine addresses capable of addressing individual storage elements. Null_Address is an address that is distinct from the address of any object or program unit.

See 13.5.3 for an explanation of Bit_Order and Default_Bit_Order.

Implementation Permissions

An implementation may add additional implementation-defined declarations to package System and its children. However, it is usually better for the implementation to provide additional functionality via implementation-defined children of System. Package System may be declared pure.

Implementation Advice

Address should be of a private type.

NOTES

(14) There are also some language-defined child packages of System defined elsewhere.

Subclauses

1. The Package System.Storage_Elements
2. The Package System.Address_To_Access_Conversions

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