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jeremybenn |
------------------------------------------------------------------------------
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-- --
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-- GNAT COMPILER COMPONENTS --
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-- --
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-- T T Y P E S --
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-- --
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-- S p e c --
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-- --
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-- Copyright (C) 1992-2009, Free Software Foundation, Inc. --
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-- --
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-- GNAT is free software; you can redistribute it and/or modify it under --
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-- terms of the GNU General Public License as published by the Free Soft- --
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-- ware Foundation; either version 3, or (at your option) any later ver- --
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-- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
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-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
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-- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
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-- for more details. You should have received a copy of the GNU General --
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-- Public License distributed with GNAT; see file COPYING3. If not, go to --
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-- http://www.gnu.org/licenses for a complete copy of the license. --
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-- --
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-- GNAT was originally developed by the GNAT team at New York University. --
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-- Extensive contributions were provided by Ada Core Technologies Inc. --
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-- --
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------------------------------------------------------------------------------
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-- This package contains constants describing target properties
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with Types; use Types;
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with Get_Targ; use Get_Targ;
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package Ttypes is
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------------------------------
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-- Host/Target Dependencies --
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------------------------------
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-- It is vital to maintain a clear distinction between properties of
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-- types on the host and types on the target, since in the general
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-- case of a cross-compiler these will be different.
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-- This package and its companion Ttypef provide definitions of values
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-- that describe the properties of the target types. All instances of
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-- target dependencies, including the definitions of such packages as
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-- Standard and System depend directly or indirectly on the definitions
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-- in the Ttypes and Ttypef packages.
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-- In the source of the compiler, references to attributes such as
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-- Integer'Size will give information regarding the host types (i.e.
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-- the types within the compiler itself). Such references are therefore
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-- almost always suspicious (it is hard for example to see that the
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-- code in the compiler should even be using type Integer very much,
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-- and certainly this code should not depend on the size of Integer).
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-- On the other hand, it is perfectly reasonable for the compiler to
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-- require access to the size of type Integer for the target machine,
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-- e.g. in constructing the internal representation of package Standard.
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-- For this purpose, instead of referencing the attribute Integer'Size,
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-- a reference to Ttypes.Standard_Integer_Size will provide the needed
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-- value for the target type.
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-- Two approaches are used for handling target dependent values in the
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-- standard library packages. Package Standard is handled specially,
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-- being constructed internally (by package Stand). Target dependent
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-- values needed in Stand are obtained by direct reference to Ttypes
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-- and Ttypef.
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-- For package System, the required constant values are obtained by
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-- referencing appropriate attributes. Ada 95 already defines most of
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-- the required attributes, and GNAT specific attributes have been
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-- defined to cover the remaining cases (such as Storage_Unit). The
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-- evaluation of these attributes obtains the required target dependent
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-- values from Ttypes and Ttypef. The additional attributes that have
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-- been added to GNAT (Address_Size, Storage_Unit, Word_Size, Max_Priority,
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-- and Max_Interrupt_Priority) are for almost all purposes redundant with
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-- respect to the corresponding references to System constants. For example
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-- in a program, System.Address_Size and Standard'Address_Size yield the
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-- same value. The critical use of the attribute is in writing the System
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-- declaration of Address_Size which of course cannot refer to itself. By
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-- this means we achieve complete target independence in the source code
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-- of package System, i.e. there is only one copy of the source of System
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-- for all targets.
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-- Note that during compilation there are two versions of package System
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-- around. The version that is directly with'ed by compiler packages
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-- contains host-dependent definitions, which is what is needed in that
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-- case (for example, System.Storage_Unit referenced in the source of the
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-- compiler refers to the storage unit of the host, not the target). This
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-- means that, like attribute references, any references to constants in
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-- package System in the compiler code are suspicious, since it is strange
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-- for the compiler to have such host dependencies. If the compiler needs
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-- to access the target dependent values of such quantities as Storage_Unit
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-- then it should reference the constants in this package (Ttypes), rather
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-- than referencing System.Storage_Unit, or Standard'Storage_Unit, both of
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-- which would yield the host value.
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---------------------------------------------------
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-- Target-Dependent Values for Types in Standard --
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---------------------------------------------------
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-- Note: GNAT always supplies all the following integer and float types,
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-- but depending on the machine, some of the types may be identical. For
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-- example, on some machines, Short_Float may be the same as Float, and
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-- Long_Long_Float may be the same as Long_Float.
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Standard_Short_Short_Integer_Size : constant Pos := Get_Char_Size;
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Standard_Short_Short_Integer_Width : constant Pos :=
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Width_From_Size (Standard_Short_Short_Integer_Size);
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Standard_Short_Integer_Size : constant Pos := Get_Short_Size;
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Standard_Short_Integer_Width : constant Pos :=
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Width_From_Size (Standard_Short_Integer_Size);
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Standard_Integer_Size : constant Pos := Get_Int_Size;
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Standard_Integer_Width : constant Pos :=
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Width_From_Size (Standard_Integer_Size);
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Standard_Long_Integer_Size : constant Pos := Get_Long_Size;
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Standard_Long_Integer_Width : constant Pos :=
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Width_From_Size (Standard_Long_Integer_Size);
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Standard_Long_Long_Integer_Size : constant Pos := Get_Long_Long_Size;
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Standard_Long_Long_Integer_Width : constant Pos :=
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Width_From_Size (Standard_Long_Long_Integer_Size);
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Standard_Short_Float_Size : constant Pos := Get_Float_Size;
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Standard_Short_Float_Digits : constant Pos :=
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Digits_From_Size (Standard_Short_Float_Size);
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Standard_Float_Size : constant Pos := Get_Float_Size;
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Standard_Float_Digits : constant Pos :=
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Digits_From_Size (Standard_Float_Size);
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Standard_Long_Float_Size : constant Pos := Get_Double_Size;
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Standard_Long_Float_Digits : constant Pos :=
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Digits_From_Size (Standard_Long_Float_Size);
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Standard_Long_Long_Float_Size : constant Pos := Get_Long_Double_Size;
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Standard_Long_Long_Float_Digits : constant Pos :=
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Digits_From_Size (Standard_Long_Long_Float_Size);
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Standard_Character_Size : constant Pos := Get_Char_Size;
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Standard_Wide_Character_Size : constant Pos := 16;
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Standard_Wide_Wide_Character_Size : constant Pos := 32;
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-- Standard wide character sizes
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-- Note: there is no specific control over the representation of
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-- enumeration types. The convention used is that if an enumeration
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-- type has fewer than 2**(Character'Size) elements, then the size
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-- used is Character'Size, otherwise Integer'Size is used.
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-- Similarly, the size of fixed-point types depends on the size of the
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-- corresponding integer type, which is the smallest predefined integer
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-- type capable of representing the required range of values.
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-------------------------------------------------
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-- Target-Dependent Values for Types in System --
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-------------------------------------------------
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System_Address_Size : constant Pos := Get_Pointer_Size;
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-- System.Address'Size (also size of all thin pointers)
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System_Max_Binary_Modulus_Power : constant Pos :=
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Standard_Long_Long_Integer_Size;
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System_Max_Nonbinary_Modulus_Power : constant Pos := Standard_Integer_Size;
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System_Storage_Unit : constant Pos := Get_Bits_Per_Unit;
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System_Word_Size : constant Pos := Get_Bits_Per_Word;
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System_Tick_Nanoseconds : constant Pos := 1_000_000_000;
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-- Value of System.Tick in nanoseconds. At the moment, this is a fixed
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-- constant (with value of 1.0 seconds), but later we should add this
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-- value to the GCC configuration file so that its value can be made
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-- configuration dependent.
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-----------------------------------------------------
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-- Target-Dependent Values for Types in Interfaces --
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-----------------------------------------------------
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Interfaces_Wchar_T_Size : constant Pos := Get_Wchar_T_Size;
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----------------------------------------
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-- Other Target-Dependent Definitions --
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----------------------------------------
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Maximum_Alignment : constant Pos := Get_Maximum_Alignment;
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-- The maximum alignment, in storage units, that an object or
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-- type may require on the target machine.
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Max_Unaligned_Field : constant Pos := Get_Max_Unaligned_Field;
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-- The maximum supported size in bits for a field that is not aligned
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-- on a storage unit boundary.
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Bytes_Big_Endian : Boolean := Get_Bytes_BE /= 0;
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-- Important note: for Ada purposes, the important setting is the bytes
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-- endianness (Bytes_Big_Endian), not the bits value (Bits_Big_Endian).
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-- This is because Ada bit addressing must be compatible with the byte
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-- ordering (otherwise we would end up with non-contiguous fields). It
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-- is rare for the two to be different, but if they are, Bits_Big_Endian
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-- is relevant only for the generation of instructions with bit numbers,
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-- and thus relevant only to the back end. Note that this is a variable
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-- rather than a constant, since it can be modified (flipped) by -gnatd8.
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Target_Strict_Alignment : Boolean := Get_Strict_Alignment /= 0;
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-- True if instructions will fail if data is misaligned
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Target_Double_Float_Alignment : Nat := Get_Double_Float_Alignment;
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-- The default alignment of "double" floating-point types, i.e. floating
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-- point types whose size is equal to 64 bits, or 0 if this alignment is
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-- not specifically capped.
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Target_Double_Scalar_Alignment : Nat := Get_Double_Scalar_Alignment;
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-- The default alignment of "double" or larger scalar types, i.e. scalar
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-- types whose size is greater or equal to 64 bits, or 0 if this alignment
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-- is not specifically capped.
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end Ttypes;
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