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-------------------------------------------------------------------------------
--- --
--- GNAT RUN-TIME COMPONENTS --
--- --
--- G N A T . B Y T E _ S W A P P I N G --
--- --
--- S p e c --
--- --
--- Copyright (C) 2006-2007, AdaCore --
--- --
--- 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, 51 Franklin Street, Fifth Floor, --
--- Boston, MA 02110-1301, 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. --
--- Extensive contributions were provided by Ada Core Technologies Inc. --
--- --
-------------------------------------------------------------------------------
-
--- Simple routines for swapping the bytes of 16-, 32-, and 64-bit objects
-
--- The generic functions should be instantiated with types that are of a size
--- in bytes corresponding to the name of the generic. For example, a 2-byte
--- integer type would be compatible with Swapped2, 4-byte integer with
--- Swapped4, and so on. Failure to do so will result in a warning when
--- compiling the instantiation; this warning should be heeded. Ignoring this
--- warning can result in unexpected results.
-
--- An example of proper usage follows:
-
--- declare
--- type Short_Integer is range -32768 .. 32767;
--- for Short_Integer'Size use 16; -- for confirmation
-
--- X : Short_Integer := 16#7FFF#;
-
--- function Swapped is new Byte_Swapping.Swapped2 (Short_Integer);
-
--- begin
--- Put_Line (X'Img);
--- X := Swapped (X);
--- Put_Line (X'Img);
--- end;
-
--- Note that the generic actual types need not be scalars, but must be
--- 'definite' types. They can, for example, be constrained subtypes of
--- unconstrained array types as long as the size is correct. For instance,
--- a subtype of String with length of 4 would be compatible with the
--- Swapped4 generic:
-
--- declare
--- subtype String4 is String (1 .. 4);
--- function Swapped is new Byte_Swapping.Swapped4 (String4);
--- S : String4 := "ABCD";
--- begin
--- Put_Line (S);
--- S := Swapped (S);
--- Put_Line (S);
--- end;
-
--- Similarly, a constrained array type is also acceptable:
-
--- declare
--- type Mask is array (0 .. 15) of Boolean;
--- for Mask'Component_Size use Boolean'Size;
--- X : Mask := (0 .. 7 => True, others => False);
--- function Swapped is new Byte_Swapping.Swapped2 (Mask);
--- begin
--- ...
--- X := Swapped (X);
--- ...
--- end;
-
--- A properly-sized record type will also be acceptable, and so forth
-
--- However, as described, a size mismatch must be avoided. In the following we
--- instantiate one of the generics with a type that is too large. The result
--- of the function call is undefined, such that assignment to an object can
--- result in garbage values.
-
--- Wrong: declare
--- subtype String16 is String (1 .. 16);
-
--- function Swapped is new Byte_Swapping.Swapped8 (String16);
--- -- Instantiation generates a compiler warning about
--- -- mismatched sizes
-
--- S : String16;
-
--- begin
--- S := "ABCDEFGHDEADBEEF";
---
--- Put_Line (S);
---
--- -- the following assignment results in garbage in S after the
--- -- first 8 bytes
---
--- S := Swapped (S);
---
--- Put_Line (S);
--- end Wrong;
-
--- When the size of the type is larger than 8 bytes, the use of the non-
--- generic procedures is an alternative because no function result is
--- involved; manipulation of the object is direct.
-
--- The procedures are passed the address of an object to manipulate. They will
--- swap the first N bytes of that object corresponding to the name of the
--- procedure. For example:
-
--- declare
--- S2 : String := "AB";
--- for S2'Alignment use 2;
--- S4 : String := "ABCD";
--- for S4'Alignment use 4;
--- S8 : String := "ABCDEFGH";
--- for S8'Alignment use 8;
-
--- begin
--- Swap2 (S2'Address);
--- Put_Line (S2);
-
--- Swap4 (S4'Address);
--- Put_Line (S4);
-
--- Swap8 (S8'Address);
--- Put_Line (S8);
--- end;
-
--- If an object of a type larger than N is passed, the remaining bytes of the
--- object are undisturbed. For example:
-
--- declare
--- subtype String16 is String (1 .. 16);
-
--- S : String16;
--- for S'Alignment use 8;
-
--- begin
--- S := "ABCDEFGHDEADBEEF";
--- Put_Line (S);
--- Swap8 (S'Address);
--- Put_Line (S);
--- end;
-
-with System;
-
-package GNAT.Byte_Swapping is
- pragma Pure;
-
- -- NB: all the routines in this package treat the application objects as
- -- unsigned (modular) types of a size in bytes corresponding to the routine
- -- name. For example, the generic function Swapped2 manipulates the object
- -- passed to the formal parameter Input as a value of an unsigned type that
- -- is 2 bytes long. Therefore clients are responsible for the compatibility
- -- of application types manipulated by these routines and these modular
- -- types, in terms of both size and alignment. This requirement applies to
- -- the generic actual type passed to the generic formal type Item in the
- -- generic functions, as well as to the type of the object implicitly
- -- designated by the address passed to the non-generic procedures. Use of
- -- incompatible types can result in implementation- defined effects.
-
- generic
- type Item is limited private;
- function Swapped2 (Input : Item) return Item;
- -- Return the 2-byte value of Input with the bytes swapped
-
- generic
- type Item is limited private;
- function Swapped4 (Input : Item) return Item;
- -- Return the 4-byte value of Input with the bytes swapped
-
- generic
- type Item is limited private;
- function Swapped8 (Input : Item) return Item;
- -- Return the 8-byte value of Input with the bytes swapped
-
- procedure Swap2 (Location : System.Address);
- -- Swap the first 2 bytes of the object starting at the address specified
- -- by Location.
-
- procedure Swap4 (Location : System.Address);
- -- Swap the first 4 bytes of the object starting at the address specified
- -- by Location.
-
- procedure Swap8 (Location : System.Address);
- -- Swap the first 8 bytes of the object starting at the address specified
- -- by Location.
-
- pragma Inline (Swap2, Swap4, Swap8, Swapped2, Swapped4, Swapped8);
-
-end GNAT.Byte_Swapping;