gcc/ada/a-stuten.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT RUN-TIME COMPONENTS                         --
   4 --                                                                          --
   5 --              A D A . S T R I N G S . U T F _ E N C O D I N G             --
   6 --                                                                          --
   7 --                                 S p e c                                  --
   8 --                                                                          --
   9 -- This specification is derived from the Ada Reference Manual for use with --
  10 -- GNAT. The copyright notice above, and the license provisions that follow --
  11 -- apply solely to the  contents of the part following the private keyword. --
  12 --                                                                          --
  13 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  14 -- terms of the  GNU General Public License as published  by the Free Soft- --
  15 -- ware  Foundation;  either version 3,  or (at your option) any later ver- --
  16 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  17 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  18 -- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
  19 --                                                                          --
  20 -- As a special exception under Section 7 of GPL version 3, you are granted --
  21 -- additional permissions described in the GCC Runtime Library Exception,   --
  22 -- version 3.1, as published by the Free Software Foundation.               --
  23 --                                                                          --
  24 -- You should have received a copy of the GNU General Public License and    --
  25 -- a copy of the GCC Runtime Library Exception along with this program;     --
  26 -- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
  27 -- <http://www.gnu.org/licenses/>.                                          --
  28 --                                                                          --
  29 -- GNAT was originally developed  by the GNAT team at  New York University. --
  30 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  31 --                                                                          --
  32 ------------------------------------------------------------------------------
  33
  34 --  This is one of the Ada 2012 package defined in AI05-0137-1. It is a parent
  35 --  package that contains declarations used in the child packages for handling
  36 --  UTF encoded strings. Note: this package is consistent with Ada 95, and may
  37 --  be used in Ada 95 or Ada 2005 mode.
  38
  39 with Interfaces;
  40 with Unchecked_Conversion;
  41
  42 package Ada.Strings.UTF_Encoding is
  43    pragma Pure (UTF_Encoding);
  44
  45    subtype UTF_String is String;
  46    --  Used to represent a string of 8-bit values containing a sequence of
  47    --  values encoded in one of three ways (UTF-8, UTF-16BE, or UTF-16LE).
  48    --  Typically used in connection with a Scheme parameter indicating which
  49    --  of the encodings applies. This is not strictly a String value in the
  50    --  sense defined in the Ada RM, but in practice type String accommodates
  51    --  all possible 256 codes, and can be used to hold any sequence of 8-bit
  52    --  codes. We use String directly rather than create a new type so that
  53    --  all existing facilities for manipulating type String (e.g. the child
  54    --  packages of Ada.Strings) are available for manipulation of UTF_Strings.
  55
  56    type Encoding_Scheme is (UTF_8, UTF_16BE, UTF_16LE);
  57    --  Used to specify which of three possible encodings apply to a UTF_String
  58
  59    subtype UTF_8_String is String;
  60    --  Similar to UTF_String but specifically represents a UTF-8 encoded string
  61
  62    subtype UTF_16_Wide_String is Wide_String;
  63    --  This is similar to UTF_8_String but is used to represent a Wide_String
  64    --  value which is a sequence of 16-bit values encoded using UTF-16. Again
  65    --  this is not strictly a Wide_String in the sense of the Ada RM, but the
  66    --  type Wide_String can be used to represent a sequence of arbitrary 16-bit
  67    --  values, and it is more convenient to use Wide_String than a new type.
  68
  69    Encoding_Error : exception;
  70    --  This exception is raised in the following situations:
  71    --    a) A UTF encoded string contains an invalid encoding sequence
  72    --    b) A UTF-16BE or UTF-16LE input string has an odd length
  73    --    c) An incorrect character value is present in the Input string
  74    --    d) The result for a Wide_Character output exceeds 16#FFFF#
  75    --  The exception message has the index value where the error occurred.
  76
  77    --  The BOM (BYTE_ORDER_MARK) values defined here are used at the start of
  78    --  a string to indicate the encoding. The convention in this package is
  79    --  that on input a correct BOM is ignored and an incorrect BOM causes an
  80    --  Encoding_Error exception. On output, the output string may or may not
  81    --  include a BOM depending on the setting of Output_BOM.
  82
  83    BOM_8    : constant UTF_8_String :=
  84                 Character'Val (16#EF#) &
  85                 Character'Val (16#BB#) &
  86                 Character'Val (16#BF#);
  87
  88    BOM_16BE : constant UTF_String :=
  89                 Character'Val (16#FE#) &
  90                 Character'Val (16#FF#);
  91
  92    BOM_16LE : constant UTF_String :=
  93                 Character'Val (16#FF#) &
  94                 Character'Val (16#FE#);
  95
  96    BOM_16   : constant UTF_16_Wide_String :=
  97                 (1 => Wide_Character'Val (16#FEFF#));
  98
  99    function Encoding
 100      (Item    : UTF_String;
 101       Default : Encoding_Scheme := UTF_8) return Encoding_Scheme;
 102    --  This function inspects a UTF_String value to determine whether it
 103    --  starts with a BOM for UTF-8, UTF-16BE, or UTF_16LE. If so, the result
 104    --  is the scheme corresponding to the BOM. If no valid BOM is present
 105    --  then the result is the specified Default value.
 106
 107 private
 108    function To_Unsigned_8 is new
 109      Unchecked_Conversion (Character, Interfaces.Unsigned_8);
 110
 111    function To_Unsigned_16 is new
 112      Unchecked_Conversion (Wide_Character, Interfaces.Unsigned_16);
 113
 114    function To_Unsigned_32 is new
 115      Unchecked_Conversion (Wide_Wide_Character, Interfaces.Unsigned_32);
 116
 117    subtype UTF_XE_Encoding is Encoding_Scheme range UTF_16BE .. UTF_16LE;
 118    --  Subtype containing only UTF_16BE and UTF_16LE entries
 119
 120    --  Utility routines for converting between UTF-16 and UTF-16LE/BE
 121
 122    function From_UTF_16
 123      (Item          : UTF_16_Wide_String;
 124       Output_Scheme : UTF_XE_Encoding;
 125       Output_BOM    : Boolean := False) return UTF_String;
 126    --  The input string Item is encoded in UTF-16. The output is encoded using
 127    --  Output_Scheme (which is either UTF-16LE or UTF-16BE). There are no error
 128    --  cases. The output starts with BOM_16BE/LE if Output_BOM is True.
 129
 130    function To_UTF_16
 131      (Item          : UTF_String;
 132       Input_Scheme  : UTF_XE_Encoding;
 133       Output_BOM    : Boolean := False) return UTF_16_Wide_String;
 134    --  The input string Item is encoded using Input_Scheme which is either
 135    --  UTF-16LE or UTF-16BE. The output is the corresponding UTF_16 wide
 136    --  string. Encoding error is raised if the length of the input is odd.
 137    --  The output starts with BOM_16 if Output_BOM is True.
 138
 139    procedure Raise_Encoding_Error (Index : Natural);
 140    pragma No_Return (Raise_Encoding_Error);
 141    --  Raise Encoding_Error exception for bad encoding in input item. The
 142    --  parameter Index is the index of the location in Item for the error.
 143
 144 end Ada.Strings.UTF_Encoding;