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13.7.1 The Package System.Storage_Elements

Static Semantics

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   The following language-defined library package exists:
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package System.Storage_Elements is
   pragma Preelaborate(System.Storage_Elements);
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   type Storage_Offset is range implementation-defined;
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   subtype Storage_Count is Storage_Offset range 0..Storage_Offset'Last;
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   type Storage_Element is mod implementation-defined;
   for Storage_Element'Size use Storage_Unit;
   type Storage_Array is array
     (Storage_Offset range <>) of aliased Storage_Element;
   for Storage_Array'Component_Size use Storage_Unit;
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   -- Address Arithmetic:
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   function "+"(Left : Address; Right : Storage_Offset)
     return Address;
   function "+"(Left : Storage_Offset; Right : Address)
     return Address;
   function "-"(Left : Address; Right : Storage_Offset)
     return Address;
   function "-"(Left, Right : Address)
     return Storage_Offset;
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   function "mod"(Left : Address; Right : Storage_Offset)
     return Storage_Offset;
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   -- Conversion to/from integers:
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   type Integer_Address is implementation-defined;
   function To_Address(Value : Integer_Address) return Address;
   function To_Integer(Value : Address) return Integer_Address;
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   pragma Convention(Intrinsic, "+");
      -- ...and so on for all language-defined subprograms declared in this package.
end System.Storage_Elements;
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    Storage_Element represents a storage element. Storage_Offset represents an offset in storage elements. Storage_Count represents a number of storage elements. Storage_Array represents a contiguous sequence of storage elements.
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    Integer_Address is a (signed or modular) integer subtype. To_Address and To_Integer convert back and forth between this type and Address.

Implementation Requirements

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    Storage_Offset'Last shall be greater than or equal to Integer'Last or the largest possible storage offset, whichever is smaller. Storage_Offset'First shall be <= (-Storage_Offset'Last).

Implementation Permissions

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    Package System.Storage_Elements may be declared pure.

Implementation Advice

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    Operations in System and its children should reflect the target environment semantics as closely as is reasonable. For example, on most machines, it makes sense for address arithmetic to ``wrap around.'' Operations that do not make sense should raise Program_Error.

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