221 lines
12 KiB
Ada
221 lines
12 KiB
Ada
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------------------------------------------------------------------------------
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-- --
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-- GNAT COMPILER COMPONENTS --
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-- --
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-- S Y S T E M . W C H _ C O N --
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-- --
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-- S p e c --
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-- --
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-- Copyright (C) 1992-2014, 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. --
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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 package defines the codes used to identify the encoding method for
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-- wide characters in string and character constants. This is needed both
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-- at compile time and at runtime (for the wide character runtime routines)
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-- This unit may be used directly from an application program by providing
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-- an appropriate WITH, and the interface can be expected to remain stable.
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pragma Compiler_Unit_Warning;
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package System.WCh_Con is
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pragma Pure;
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-------------------------------------
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-- Wide_Character Encoding Methods --
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-------------------------------------
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-- A wide character encoding method is a method for uniquely representing
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-- a Wide_Character or Wide_Wide_Character value using a one or more
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-- Character values. Three types of encoding method are supported by GNAT:
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-- An escape encoding method uses ESC as the first character of the
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-- sequence, and subsequent characters determine the wide character
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-- value that is represented. Any character other than ESC stands
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-- for itself as a single byte (i.e. any character in Latin-1, other
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-- than ESC itself, is represented as a single character: itself).
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-- An upper half encoding method uses a character in the upper half
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-- range (i.e. in the range 16#80# .. 16#FF#) as the first byte of
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-- a wide character encoding sequence. Subsequent characters are
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-- used to determine the wide character value that is represented.
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-- Any character in the lower half (16#00# .. 16#7F#) represents
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-- itself as a single character.
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-- The brackets notation, where a wide character is represented by the
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-- sequence ["xx"] or ["xxxx"] or ["xxxxxx"] where xx are hexadecimal
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-- characters. Note that currently this is the only encoding that
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-- supports the full UTF-32 range.
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-- Note that GNAT does not currently support escape-in, escape-out
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-- encoding methods, where an escape sequence is used to set a mode
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-- used to recognize subsequent characters. All encoding methods use
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-- individual character-by-character encodings, so that a sequence of
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-- wide characters is represented by a sequence of encodings.
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-- To add new encoding methods, the following steps are required:
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-- 1. Define a code for a new value of type WC_Encoding_Method
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-- 2. Adjust the definition of WC_Encoding_Method accordingly
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-- 3. Provide appropriate conversion routines in System.WCh_Cnv
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-- 4. Adjust definition of WC_Longest_Sequence if necessary
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-- 5. Add an entry in WC_Encoding_Letters for the new method
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-- 6. Add proper code to s-wchstw.adb, s-wchwts.adb, s-widwch.adb
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-- 7. Update documentation (remember section on form strings)
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-- Note that the WC_Encoding_Method values must be kept ordered so that
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-- the definitions of the subtypes WC_Upper_Half_Encoding_Method and
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-- WC_ESC_Encoding_Method are still correct.
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---------------------------------
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-- Encoding Method Definitions --
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---------------------------------
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type WC_Encoding_Method is range 1 .. 6;
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-- Type covering the range of values used to represent wide character
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-- encoding methods. An enumeration type might be a little neater, but
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-- more trouble than it's worth, given the need to pass these values
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-- from the compiler to the backend, and to record them in the ALI file.
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WCEM_Hex : constant WC_Encoding_Method := 1;
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-- The wide character with code 16#abcd# is represented by the escape
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-- sequence ESC a b c d (five characters, where abcd are ASCII hex
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-- characters, using upper case for letters). This method is easy
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-- to deal with in external environments that do not support wide
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-- characters, and covers the whole 16-bit BMP. Codes larger than
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-- 16#FFFF# are not representable using this encoding method.
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WCEM_Upper : constant WC_Encoding_Method := 2;
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-- The wide character with encoding 16#abcd#, where the upper bit is on
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-- (i.e. a is in the range 8-F) is represented as two bytes 16#ab# and
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-- 16#cd#. The second byte may never be a format control character, but
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-- is not required to be in the upper half. This method can be also used
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-- for shift-JIS or EUC where the internal coding matches the external
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-- coding. Codes larger than 16#FFFF# are not representable using this
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-- encoding method.
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WCEM_Shift_JIS : constant WC_Encoding_Method := 3;
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-- A wide character is represented by a two character sequence 16#ab#
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-- and 16#cd#, with the restrictions described for upper half encoding
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-- as described above. The internal character code is the corresponding
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-- JIS character according to the standard algorithm for Shift-JIS
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-- conversion. See the body of package System.JIS_Conversions for
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-- further details. Codes larger than 16#FFFF are not representable
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-- using this encoding method.
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WCEM_EUC : constant WC_Encoding_Method := 4;
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-- A wide character is represented by a two character sequence 16#ab# and
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-- 16#cd#, with both characters being in the upper half set. The internal
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-- character code is the corresponding JIS character according to the EUC
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-- encoding algorithm. See the body of package System.JIS_Conversions for
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-- further details. Codes larger than 16#FFFF# are not representable using
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-- this encoding method.
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WCEM_UTF8 : constant WC_Encoding_Method := 5;
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-- An ISO 10646-1 BMP/Unicode wide character is represented in UCS
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-- Transformation Format 8 (UTF-8), as defined in Annex R of ISO
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-- 10646-1/Am.2. Depending on the character value, a Unicode character
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-- is represented as the one to six byte sequence.
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--
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-- 16#0000_0000#-16#0000_007f#: 2#0xxxxxxx#
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-- 16#0000_0080#-16#0000_07ff#: 2#110xxxxx# 2#10xxxxxx#
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-- 16#0000_0800#-16#0000_ffff#: 2#1110xxxx# 2#10xxxxxx# 2#10xxxxxx#
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-- 16#0001_0000#-16#001F_FFFF#: 2#11110xxx# 2#10xxxxxx# 2#10xxxxxx#
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-- 2#10xxxxxx#
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-- 16#0020_0000#-16#03FF_FFFF#: 2#111110xx# 2#10xxxxxx# 2#10xxxxxx#
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-- 2#10xxxxxx# 2#10xxxxxx#
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-- 16#0400_0000#-16#7FFF_FFFF#: 2#1111110x# 2#10xxxxxx# 2#10xxxxxx#
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-- 2#10xxxxxx# 2#10xxxxxx# 2#10xxxxxx#
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--
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-- where the xxx bits correspond to the left-padded bits of the
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-- 16-bit character value. Note that all lower half ASCII characters
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-- are represented as ASCII bytes and all upper half characters and
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-- other wide characters are represented as sequences of upper-half. This
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-- encoding method can represent the entire range of Wide_Wide_Character.
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WCEM_Brackets : constant WC_Encoding_Method := 6;
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-- A wide character is represented using one of the following sequences:
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--
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-- ["xx"]
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-- ["xxxx"]
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-- ["xxxxxx"]
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-- ["xxxxxxxx"]
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--
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-- where xx are hexadecimal digits representing the character code. This
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-- encoding method can represent the entire range of Wide_Wide_Character
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-- but in the general case results in ambiguous representations (there is
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-- no ambiguity in Ada sources, since the above sequences are illegal Ada).
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WC_Encoding_Letters : constant array (WC_Encoding_Method) of Character :=
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(WCEM_Hex => 'h',
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WCEM_Upper => 'u',
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WCEM_Shift_JIS => 's',
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WCEM_EUC => 'e',
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WCEM_UTF8 => '8',
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WCEM_Brackets => 'b');
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-- Letters used for selection of wide character encoding method in the
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-- compiler options (-gnatW? switch) and for Wide_Text_IO (WCEM parameter
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-- in the form string).
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subtype WC_ESC_Encoding_Method is
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WC_Encoding_Method range WCEM_Hex .. WCEM_Hex;
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-- Encoding methods using an ESC character at the start of the sequence
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subtype WC_Upper_Half_Encoding_Method is
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WC_Encoding_Method range WCEM_Upper .. WCEM_UTF8;
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-- Encoding methods using an upper half character (16#80#..16#FF) at
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-- the start of the sequence.
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WC_Longest_Sequence : constant := 12;
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-- The longest number of characters that can be used for a wide character
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-- or wide wide character sequence for any of the active encoding methods.
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WC_Longest_Sequences : constant array (WC_Encoding_Method) of Natural :=
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(WCEM_Hex => 5,
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WCEM_Upper => 2,
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WCEM_Shift_JIS => 2,
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WCEM_EUC => 2,
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WCEM_UTF8 => 6,
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WCEM_Brackets => 12);
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-- The longest number of characters that can be used for a wide character
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-- or wide wide character sequence using the given encoding method.
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function Get_WC_Encoding_Method (C : Character) return WC_Encoding_Method;
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-- Given a character C, returns corresponding encoding method (see array
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-- WC_Encoding_Letters above). Raises Constraint_Error if not in list.
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function Get_WC_Encoding_Method (S : String) return WC_Encoding_Method;
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-- Given a lower case string that is one of hex, upper, shift_jis, euc,
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-- utf8, brackets, return the corresponding encoding method. Raises
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-- Constraint_Error if not in list.
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function Is_Start_Of_Encoding
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(C : Character;
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EM : WC_Encoding_Method) return Boolean;
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pragma Inline (Is_Start_Of_Encoding);
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-- Returns True if the Character C is the start of a multi-character
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-- encoding sequence for the given encoding method EM. If EM is set to
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-- WCEM_Brackets, this function always returns False.
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end System.WCh_Con;
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