177 lines
10 KiB
Ada
177 lines
10 KiB
Ada
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------------------------------------------------------------------------------
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-- --
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-- GNAT RUN-TIME COMPONENTS --
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-- --
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-- G N A T . D E C O D E _ S T R I N G --
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-- --
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-- S p e c --
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-- --
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-- Copyright (C) 2007-2013, AdaCore --
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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. --
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-- --
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-- As a special exception under Section 7 of GPL version 3, you are granted --
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-- additional permissions described in the GCC Runtime Library Exception, --
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-- version 3.1, as published by the Free Software Foundation. --
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-- --
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-- You should have received a copy of the GNU General Public License and --
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-- a copy of the GCC Runtime Library Exception along with this program; --
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-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
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-- <http://www.gnu.org/licenses/>. --
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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 generic package provides utility routines for converting from an
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-- encoded string to a corresponding Wide_String or Wide_Wide_String value
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-- using a specified encoding convention, which is supplied as the generic
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-- parameter. UTF-8 is handled especially efficiently, and if the encoding
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-- method is known at compile time to be WCEM_UTF8, then the instantiation
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-- is specialized to handle only the UTF-8 case and exclude code for the
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-- other encoding methods. The package also provides positioning routines
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-- for skipping encoded characters in either direction, and for validating
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-- strings for correct encodings.
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-- Note: this package is only about decoding sequences of 8-bit characters
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-- into corresponding 16-bit Wide_String or 32-bit Wide_Wide_String values.
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-- It knows nothing at all about the character encodings being used for the
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-- resulting Wide_Character and Wide_Wide_Character values. Most often this
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-- will be Unicode/ISO-10646 as specified by the Ada RM, but this package
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-- does not make any assumptions about the character coding. See also the
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-- packages Ada.Wide_[Wide_]Characters.Unicode for unicode specific functions.
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-- In particular, in the case of UTF-8, all valid UTF-8 encodings, as listed
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-- in table 3.6 of the Unicode Standard, version 6.2.0, are recognized as
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-- legitimate. This includes the full range 16#0000_0000# .. 16#03FF_FFFF#.
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-- This includes codes in the range 16#D800# - 16#DFFF#. These codes all
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-- have UTF-8 encoding sequences that are well-defined (e.g. the encoding for
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-- 16#D800# is ED A0 80). But these codes do not correspond to defined Unicode
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-- characters and are thus considered to be "not well-formed" (see table 3.7
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-- of the Unicode Standard). If you need to exclude these codes, you must do
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-- that manually, e.g. use Decode_Wide_Character/Decode_Wide_String and check
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-- that the resulting code(s) are not in this range.
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-- Note on the use of brackets encoding (WCEM_Brackets). The brackets encoding
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-- method is ambiguous in the context of this package, since there is no way
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-- to tell if ["1234"] is eight unencoded characters or one encoded character.
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-- In the context of Ada sources, any sequence starting [" must be the start
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-- of an encoding (since that sequence is not valid in Ada source otherwise).
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-- The routines in this package use the same approach. If the input string
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-- contains the sequence [" then this is assumed to be the start of a brackets
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-- encoding sequence, and if it does not match the syntax, an error is raised.
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-- In the case of the Prev functions, a sequence ending with "] is assumed to
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-- be a valid brackets sequence, and an error is raised if it is not.
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with System.WCh_Con;
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generic
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Encoding_Method : System.WCh_Con.WC_Encoding_Method;
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package GNAT.Decode_String is
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pragma Pure;
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function Decode_Wide_String (S : String) return Wide_String;
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pragma Inline (Decode_Wide_String);
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-- Decode the given String, which is encoded using the indicated coding
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-- method, returning the corresponding decoded Wide_String value. If S
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-- contains a character code that cannot be represented with the given
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-- encoding, then Constraint_Error is raised.
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procedure Decode_Wide_String
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(S : String;
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Result : out Wide_String;
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Length : out Natural);
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-- Similar to the above function except that the result is stored in the
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-- given Wide_String variable Result, starting at Result (Result'First). On
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-- return, Length is set to the number of characters stored in Result. The
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-- caller must ensure that Result is long enough (an easy choice is to set
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-- the length equal to the S'Length, since decoding can never increase the
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-- string length). If the length of Result is insufficient Constraint_Error
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-- will be raised.
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function Decode_Wide_Wide_String (S : String) return Wide_Wide_String;
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-- Same as above function but for Wide_Wide_String output
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procedure Decode_Wide_Wide_String
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(S : String;
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Result : out Wide_Wide_String;
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Length : out Natural);
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-- Same as above procedure, but for Wide_Wide_String output
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function Validate_Wide_String (S : String) return Boolean;
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-- This function inspects the string S to determine if it contains only
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-- valid encodings corresponding to Wide_Character values using the
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-- given encoding. If a call to Decode_Wide_String (S) would return
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-- without raising Constraint_Error, then Validate_Wide_String will
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-- return True. If the call would have raised Constraint_Error, then
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-- Validate_Wide_String will return False.
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function Validate_Wide_Wide_String (S : String) return Boolean;
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-- Similar to Validate_Wide_String, except that it succeeds if the string
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-- contains only encodings corresponding to Wide_Wide_Character values.
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procedure Decode_Wide_Character
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(Input : String;
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Ptr : in out Natural;
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Result : out Wide_Character);
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pragma Inline (Decode_Wide_Character);
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-- This is a lower level procedure that decodes a single character using
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-- the given encoding method. The encoded character is stored in Input,
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-- starting at Input (Ptr). The resulting output character is stored in
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-- Result, and on return Ptr is updated past the input character or
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-- encoding sequence. Constraint_Error will be raised if the input has
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-- has a character that cannot be represented using the given encoding,
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-- or if Ptr is outside the bounds of the Input string.
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procedure Decode_Wide_Wide_Character
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(Input : String;
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Ptr : in out Natural;
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Result : out Wide_Wide_Character);
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pragma Inline (Decode_Wide_Wide_Character);
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-- Same as above procedure but with Wide_Wide_Character input
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procedure Next_Wide_Character (Input : String; Ptr : in out Natural);
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pragma Inline (Next_Wide_Character);
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-- This procedure examines the input string starting at Input (Ptr), and
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-- advances Ptr past one character in the encoded string, so that on return
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-- Ptr points to the next encoded character. Constraint_Error is raised if
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-- an invalid encoding is encountered, or the end of the string is reached
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-- or if Ptr is less than String'First on entry, or if the character
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-- skipped is not a valid Wide_Character code.
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procedure Prev_Wide_Character (Input : String; Ptr : in out Natural);
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-- This procedure is similar to Next_Encoded_Character except that it moves
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-- backwards in the string, so that on return, Ptr is set to point to the
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-- previous encoded character. Constraint_Error is raised if the start of
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-- the string is encountered. It is valid for Ptr to be one past the end
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-- of the string for this call (in which case on return it will point to
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-- the last encoded character).
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--
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-- Note: it is not generally possible to do this function efficiently with
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-- all encodings, the current implementation is only efficient for the case
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-- of UTF-8 (Encoding_Method = WCEM_UTF8) and Brackets (Encoding_Method =
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-- WCEM_Brackets). For all other encodings, we work by starting at the
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-- beginning of the string and moving forward till Ptr is reached, which
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-- is correct but slow.
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--
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-- Note: this routine assumes that the sequence prior to Ptr is correctly
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-- encoded, it does not have a defined behavior if this is not the case.
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procedure Next_Wide_Wide_Character (Input : String; Ptr : in out Natural);
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pragma Inline (Next_Wide_Wide_Character);
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-- Similar to Next_Wide_Character except that codes skipped must be valid
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-- Wide_Wide_Character codes.
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procedure Prev_Wide_Wide_Character (Input : String; Ptr : in out Natural);
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-- Similar to Prev_Wide_Character except that codes skipped must be valid
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-- Wide_Wide_Character codes.
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end GNAT.Decode_String;
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