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-- --
-- --
-- A D A . S T R I N G S . U T F _ E N C O D I N G --
-- --
-- S p e c --
-- --
-- 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 3, 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 --
-- --
-- As a special exception under Section 7 of GPL version 3, you are granted --
-- additional permissions described in the GCC Runtime Library Exception, --
-- version 3.1, as published by the Free Software Foundation. --
-- --
-- You should have received a copy of the GNU General Public License and --
-- a copy of the GCC Runtime Library Exception along with this program; --
-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
-- <>. --
-- --
-- GNAT was originally developed by the GNAT team at New York University. --
-- Extensive contributions were provided by Ada Core Technologies Inc. --
-- --
-- This is one of the Ada 2012 package defined in AI05-0137-1. It is a parent
-- package that contains declarations used in the child packages for handling
-- UTF encoded strings. Note: this package is consistent with Ada 95, and may
-- be used in Ada 95 or Ada 2005 mode.
with Interfaces;
with Unchecked_Conversion;
package Ada.Strings.UTF_Encoding is
pragma Pure (UTF_Encoding);
subtype UTF_String is String;
-- Used to represent a string of 8-bit values containing a sequence of
-- values encoded in one of three ways (UTF-8, UTF-16BE, or UTF-16LE).
-- Typically used in connection with a Scheme parameter indicating which
-- of the encodings applies. This is not strictly a String value in the
-- sense defined in the Ada RM, but in practice type String accommodates
-- all possible 256 codes, and can be used to hold any sequence of 8-bit
-- codes. We use String directly rather than create a new type so that
-- all existing facilities for manipulating type String (e.g. the child
-- packages of Ada.Strings) are available for manipulation of UTF_Strings.
type Encoding_Scheme is (UTF_8, UTF_16BE, UTF_16LE);
-- Used to specify which of three possible encodings apply to a UTF_String
subtype UTF_8_String is String;
-- Similar to UTF_String but specifically represents a UTF-8 encoded string
subtype UTF_16_Wide_String is Wide_String;
-- This is similar to UTF_8_String but is used to represent a Wide_String
-- value which is a sequence of 16-bit values encoded using UTF-16. Again
-- this is not strictly a Wide_String in the sense of the Ada RM, but the
-- type Wide_String can be used to represent a sequence of arbitrary 16-bit
-- values, and it is more convenient to use Wide_String than a new type.
Encoding_Error : exception;
-- This exception is raised in the following situations:
-- a) A UTF encoded string contains an invalid encoding sequence
-- b) A UTF-16BE or UTF-16LE input string has an odd length
-- c) An incorrect character value is present in the Input string
-- d) The result for a Wide_Character output exceeds 16#FFFF#
-- The exception message has the index value where the error occurred.
-- The BOM (BYTE_ORDER_MARK) values defined here are used at the start of
-- a string to indicate the encoding. The convention in this package is
-- that on input a correct BOM is ignored and an incorrect BOM causes an
-- Encoding_Error exception. On output, the output string may or may not
-- include a BOM depending on the setting of Output_BOM.
BOM_8 : constant UTF_8_String :=
Character'Val (16#EF#) &
Character'Val (16#BB#) &
Character'Val (16#BF#);
BOM_16BE : constant UTF_String :=
Character'Val (16#FE#) &
Character'Val (16#FF#);
BOM_16LE : constant UTF_String :=
Character'Val (16#FF#) &
Character'Val (16#FE#);
BOM_16 : constant UTF_16_Wide_String :=
(1 => Wide_Character'Val (16#FEFF#));
function Encoding
(Item : UTF_String;
Default : Encoding_Scheme := UTF_8) return Encoding_Scheme;
-- This function inspects a UTF_String value to determine whether it
-- starts with a BOM for UTF-8, UTF-16BE, or UTF_16LE. If so, the result
-- is the scheme corresponding to the BOM. If no valid BOM is present
-- then the result is the specified Default value.
function To_Unsigned_8 is new
Unchecked_Conversion (Character, Interfaces.Unsigned_8);
function To_Unsigned_16 is new
Unchecked_Conversion (Wide_Character, Interfaces.Unsigned_16);
function To_Unsigned_32 is new
Unchecked_Conversion (Wide_Wide_Character, Interfaces.Unsigned_32);
subtype UTF_XE_Encoding is Encoding_Scheme range UTF_16BE .. UTF_16LE;
-- Subtype containing only UTF_16BE and UTF_16LE entries
-- Utility routines for converting between UTF-16 and UTF-16LE/BE
function From_UTF_16
(Item : UTF_16_Wide_String;
Output_Scheme : UTF_XE_Encoding;
Output_BOM : Boolean := False) return UTF_String;
-- The input string Item is encoded in UTF-16. The output is encoded using
-- Output_Scheme (which is either UTF-16LE or UTF-16BE). There are no error
-- cases. The output starts with BOM_16BE/LE if Output_BOM is True.
function To_UTF_16
(Item : UTF_String;
Input_Scheme : UTF_XE_Encoding;
Output_BOM : Boolean := False) return UTF_16_Wide_String;
-- The input string Item is encoded using Input_Scheme which is either
-- UTF-16LE or UTF-16BE. The output is the corresponding UTF_16 wide
-- string. Encoding error is raised if the length of the input is odd.
-- The output starts with BOM_16 if Output_BOM is True.
procedure Raise_Encoding_Error (Index : Natural);
pragma No_Return (Raise_Encoding_Error);
-- Raise Encoding_Error exception for bad encoding in input item. The
-- parameter Index is the index of the location in Item for the error.
end Ada.Strings.UTF_Encoding;