File : unicode-ces-utf16.ads
-----------------------------------------------------------------------
-- XML/Ada - An XML suite for Ada95 --
-- --
-- Copyright (C) 2001 --
-- ACT-Europe --
-- Author: Emmanuel Briot --
-- --
-- This library is free software; you can redistribute it and/or --
-- modify it under the terms of the GNU General Public --
-- License as published by the Free Software Foundation; either --
-- version 2 of the License, or (at your option) any later version. --
-- --
-- This library is distributed in the hope that it will be useful, --
-- but WITHOUT 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 along with this library; if not, write to the --
-- Free Software Foundation, Inc., 59 Temple Place - Suite 330, --
-- Boston, MA 02111-1307, 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. --
-----------------------------------------------------------------------
-- This package provides support for Utf16 encoding of characters.
--
-- Although utf32 is simpler, it requires too much space to encode typical
-- strings. Indeed, only two bytes are currently needed to encode every
-- unicode character. Thus, utf16 was created in that purpose. Most characters
-- are encoded only on two bytes, although there is provision for a four-byte
-- encoding in some cases, using what is known as surrogate pairs.
--
-- As a result, utf16 is a variable-width encoding, and traversing a string is
-- a little bit less efficient that with Utf32.
--
-- Another inconvenient is that you can not easily search an ASCII character
-- in a string with the standard string manipulation functions, since you
-- might find the high-byte of a two-byte sequence.
with Unicode.CES.Utf32;
with Unicode.CCS;
with Unchecked_Deallocation;
package Unicode.CES.Utf16 is
-----------
-- Types --
-----------
subtype Utf16_String is String;
type Utf16_String_Access is access Utf16_String;
-- A UTF16-encoded string, undefined byte-order
subtype Utf16_LE_String is Utf16_String;
type Utf16_LE_String_Access is access Utf16_LE_String;
-- Similar, but with little-endian byte-order
subtype Utf16_BE_String is Utf16_String;
-- Similar, but with big-endian byte-order
-------------------------------------------
-- Conversion to and from byte sequences --
-------------------------------------------
function Encode (Char : Unicode_Char) return Utf16_LE_String;
-- Return the byte sequence representing Char in the Utf16 character
-- encoding form (little-endian)
function Read (Str : Utf16_LE_String; Index : Positive) return Unicode_Char;
-- Return the character starting at location Index in Str
function Read_BE (Str : Utf16_BE_String; Index : Positive)
return Unicode_Char;
-- Return the character starting at location Index in Str (big-endian)
function Encode_BE (Char : Unicode_Char) return Utf16_BE_String;
-- Return the byte sequence representing Char in the Utf16 character
-- encoding form (big-endian)
function Width (Char : Unicode_Char) return Natural;
-- Return the number of bytes occupied by the Utf16 representation of Char
function Length (Str : Utf16_String) return Natural;
-- Return the number of characters in Str
-------------------------------------------
-- Conversion to and from Utf32-encoding --
-------------------------------------------
function From_Utf32
(Str : Unicode.CES.Utf32.Utf32_LE_String)
return Utf16_LE_String;
-- Return a new utf16-encoded string, from a Utf32-encoded string.
function To_Utf32
(Str : Utf16_LE_String)
return Unicode.CES.Utf32.Utf32_LE_String;
-- Return a new utf32-encoded string, from a Utf16-encoded string.
---------------------------
-- Byte order conversion --
---------------------------
function To_Unicode_LE
(Str : Utf16_String;
Cs : Unicode.CCS.Character_Set := Unicode.CCS.Unicode_Character_Set;
Order : Byte_Order := Default_Byte_Order) return Utf16_LE_String;
-- Convert Str to a Unicode, little-endian utf16-encoding byte sequence.
-- Order is the order in which bytes are coded in Str. This is silently
-- overriden in case Str as a BOM (byte-order-marker) at the beginning
-- that specifies an explicit order.
-- The BOM is removed from the resulting string
-- Invalid_Encoding is raised if Str contains a BOM that indicates an
-- encoding other than Utf16.
function To_CS
(Str : Utf16_LE_String;
Cs : Unicode.CCS.Character_Set := Unicode.CCS.Unicode_Character_Set;
Order : Byte_Order := Default_Byte_Order) return Utf16_String;
-- Convert Str from Unicode to another character set, and possibly
-- another ordering.
-- No BOM is checked
---------------------
-- Encoding Scheme --
---------------------
Utf16_LE_Encoding : constant Encoding_Scheme :=
(Read => Read'Access,
Width => Width'Access,
Encode => Encode_Function' (Encode'Access),
Length => Length'Access);
Utf16_BE_Encoding : constant Encoding_Scheme :=
(Read => Read_BE'Access,
Width => Width'Access,
Encode => Encode_Function' (Encode_BE'Access),
Length => Length'Access);
------------------
-- Deallocation --
------------------
procedure Free is new Unchecked_Deallocation
(Utf16_String, Utf16_String_Access);
procedure Free is new Unchecked_Deallocation
(Utf16_LE_String, Utf16_LE_String_Access);
-- Free the memory occupied by a utf16-encoded string
private
pragma Inline (Width);
end Unicode.CES.Utf16;