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------------------------------------------------------------------------------
--                                                                          --
--                         GNAT RUN-TIME COMPONENTS                         --
--                                                                          --
--                   ADA.STRINGS.UTF_ENCODING.CONVERSIONS                   --
--                                                                          --
--                                 B o d y                                  --
--                                                                          --
--          Copyright (C) 2010-2011, Free Software Foundation, Inc.         --
--                                                                          --
-- 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 --
-- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
--                                                                          --
-- 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    --
-- <http://www.gnu.org/licenses/>.                                          --
--                                                                          --
-- GNAT was originally developed  by the GNAT team at  New York University. --
-- Extensive contributions were provided by Ada Core Technologies Inc.      --
--                                                                          --
------------------------------------------------------------------------------
 
package body Ada.Strings.UTF_Encoding.Conversions is
   use Interfaces;
 
   --  Convert from UTF-8/UTF-16BE/LE to UTF-8/UTF-16BE/LE
 
   function Convert
     (Item          : UTF_String;
      Input_Scheme  : Encoding_Scheme;
      Output_Scheme : Encoding_Scheme;
      Output_BOM    : Boolean := False) return UTF_String
   is
   begin
      --  Nothing to do if identical schemes
 
      if Input_Scheme = Output_Scheme then
         return Item;
 
      --  For remaining cases, one or other of the operands is UTF-16BE/LE
      --  encoded, so go through UTF-16 intermediate.
 
      else
         return Convert (UTF_16_Wide_String'(Convert (Item, Input_Scheme)),
                         Output_Scheme, Output_BOM);
      end if;
   end Convert;
 
   --  Convert from UTF-8/UTF-16BE/LE to UTF-16
 
   function Convert
     (Item          : UTF_String;
      Input_Scheme  : Encoding_Scheme;
      Output_BOM    : Boolean := False) return UTF_16_Wide_String
   is
   begin
      if Input_Scheme = UTF_8 then
         return Convert (Item, Output_BOM);
      else
         return To_UTF_16 (Item, Input_Scheme, Output_BOM);
      end if;
   end Convert;
 
   --  Convert from UTF-8 to UTF-16
 
   function Convert
     (Item       : UTF_8_String;
      Output_BOM : Boolean := False) return UTF_16_Wide_String
   is
      Result : UTF_16_Wide_String (1 .. Item'Length + 1);
      --  Maximum length of result, including possible BOM
 
      Len : Natural := 0;
      --  Number of characters stored so far in Result
 
      Iptr : Natural;
      --  Next character to process in Item
 
      C : Unsigned_8;
      --  Input UTF-8 code
 
      R : Unsigned_16;
      --  Output UTF-16 code
 
      procedure Get_Continuation;
      --  Reads a continuation byte of the form 10xxxxxx, shifts R left by 6
      --  bits, and or's in the xxxxxx to the low order 6 bits. On return Ptr
      --  is incremented. Raises exception if continuation byte does not exist
      --  or is invalid.
 
      ----------------------
      -- Get_Continuation --
      ----------------------
 
      procedure Get_Continuation is
      begin
         if Iptr > Item'Last then
            Raise_Encoding_Error (Iptr - 1);
 
         else
            C := To_Unsigned_8 (Item (Iptr));
            Iptr := Iptr + 1;
 
            if C < 2#10_000000# or else C > 2#10_111111# then
               Raise_Encoding_Error (Iptr - 1);
 
            else
               R :=
                 Shift_Left (R, 6) or Unsigned_16 (C and 2#00_111111#);
            end if;
         end if;
      end Get_Continuation;
 
   --  Start of processing for Convert
 
   begin
      --  Output BOM if required
 
      if Output_BOM then
         Len := Len + 1;
         Result (Len) := BOM_16 (1);
      end if;
 
      --  Skip OK BOM
 
      Iptr := Item'First;
 
      if Item'Length >= 3 and then Item (Iptr .. Iptr + 2) = BOM_8 then
         Iptr := Iptr + 3;
 
      --  Error if bad BOM
 
      elsif Item'Length >= 2
        and then (Item (Iptr .. Iptr + 1) = BOM_16BE
                    or else
                  Item (Iptr .. Iptr + 1) = BOM_16LE)
      then
         Raise_Encoding_Error (Iptr);
 
      --  No BOM present
 
      else
         Iptr := Item'First;
      end if;
 
      while Iptr <= Item'Last loop
         C := To_Unsigned_8 (Item (Iptr));
         Iptr := Iptr + 1;
 
         --  Codes in the range 16#00# - 16#7F#
         --    UTF-8:  0xxxxxxx
         --    UTF-16: 00000000_0xxxxxxx
 
         if C <= 16#7F# then
            Len := Len + 1;
            Result (Len) := Wide_Character'Val (C);
 
         --  No initial code can be of the form 10xxxxxx. Such codes are used
         --  only for continuations.
 
         elsif C <= 2#10_111111# then
            Raise_Encoding_Error (Iptr - 1);
 
         --  Codes in the range 16#80# - 16#7FF#
         --    UTF-8:  110yyyxx 10xxxxxx
         --    UTF-16: 00000yyy_xxxxxxxx
 
         elsif C <= 2#110_11111# then
            R := Unsigned_16 (C and 2#000_11111#);
            Get_Continuation;
            Len := Len + 1;
            Result (Len) := Wide_Character'Val (R);
 
         --  Codes in the range 16#800# - 16#FFFF#
         --    UTF-8:  1110yyyy 10yyyyxx 10xxxxxx
         --    UTF-16: yyyyyyyy_xxxxxxxx
 
         elsif C <= 2#1110_1111# then
            R := Unsigned_16 (C and 2#0000_1111#);
            Get_Continuation;
            Get_Continuation;
            Len := Len + 1;
            Result (Len) := Wide_Character'Val (R);
 
            --  Make sure that we don't have a result in the forbidden range
            --  reserved for UTF-16 surrogate characters.
 
            if R in 16#D800# .. 16#DF00# then
               Raise_Encoding_Error (Iptr - 3);
            end if;
 
         --  Codes in the range 16#10000# - 16#10FFFF#
         --    UTF-8:  11110zzz 10zzyyyy 10yyyyxx 10xxxxxx
         --    UTF-16: 110110zz_zzyyyyyy 110111yy_xxxxxxxx
         --    Note: zzzz in the output is input zzzzz - 1
 
         elsif C <= 2#11110_111# then
            R := Unsigned_16 (C and 2#00000_111#);
            Get_Continuation;
 
            --  R now has zzzzzyyyy
 
            R := R - 2#0000_1_0000#;
 
            --  R now has zzzzyyyy (zzzz minus one for the output)
 
            Get_Continuation;
 
            --  R now has zzzzyyyyyyyyxx
 
            Len := Len + 1;
            Result (Len) :=
              Wide_Character'Val
                (2#110110_00_0000_0000# or Shift_Right (R, 4));
 
            R := R and 2#1111#;
            Get_Continuation;
            Len := Len + 1;
            Result (Len) :=
              Wide_Character'Val (2#110111_00_0000_0000# or R);
 
         --  Any other code is an error
 
         else
            Raise_Encoding_Error (Iptr - 1);
         end if;
      end loop;
 
      return Result (1 .. Len);
   end Convert;
 
   --  Convert from UTF-16 to UTF-8/UTF-16-BE/LE
 
   function Convert
     (Item          : UTF_16_Wide_String;
      Output_Scheme : Encoding_Scheme;
      Output_BOM    : Boolean := False) return UTF_String
   is
   begin
      if Output_Scheme = UTF_8 then
         return Convert (Item, Output_BOM);
      else
         return From_UTF_16 (Item, Output_Scheme, Output_BOM);
      end if;
   end Convert;
 
   --  Convert from UTF-16 to UTF-8
 
   function Convert
     (Item          : UTF_16_Wide_String;
      Output_BOM    : Boolean := False) return UTF_8_String
   is
      Result : UTF_8_String (1 .. 3 * Item'Length + 3);
      --  Worst case is 3 output codes for each input code + BOM space
 
      Len : Natural;
      --  Number of result codes stored
 
      Iptr : Natural;
      --  Pointer to next input character
 
      C1, C2 : Unsigned_16;
 
      zzzzz    : Unsigned_16;
      yyyyyyyy : Unsigned_16;
      xxxxxxxx : Unsigned_16;
      --  Components of double length case
 
   begin
      Iptr := Item'First;
 
      --  Skip BOM at start of input
 
      if Item'Length > 0 and then Item (Iptr) = BOM_16 (1) then
         Iptr := Iptr + 1;
      end if;
 
      --  Generate output BOM if required
 
      if Output_BOM then
         Result (1 .. 3) := BOM_8;
         Len := 3;
      else
         Len := 0;
      end if;
 
      --  Loop through input
 
      while Iptr <= Item'Last loop
         C1 := To_Unsigned_16 (Item (Iptr));
         Iptr := Iptr + 1;
 
         --  Codes in the range 16#0000# - 16#007F#
         --    UTF-16: 000000000xxxxxxx
         --    UTF-8:  0xxxxxxx
 
         if C1 <= 16#007F# then
            Result (Len + 1) := Character'Val (C1);
            Len := Len + 1;
 
         --  Codes in the range 16#80# - 16#7FF#
         --    UTF-16: 00000yyyxxxxxxxx
         --    UTF-8:  110yyyxx 10xxxxxx
 
         elsif C1 <= 16#07FF# then
            Result (Len + 1) :=
              Character'Val
                (2#110_00000# or Shift_Right (C1, 6));
            Result (Len + 2) :=
              Character'Val
                (2#10_000000# or (C1 and 2#00_111111#));
            Len := Len + 2;
 
         --  Codes in the range 16#800# - 16#D7FF# or 16#E000# - 16#FFFF#
         --    UTF-16: yyyyyyyyxxxxxxxx
         --    UTF-8:  1110yyyy 10yyyyxx 10xxxxxx
 
         elsif C1 <= 16#D7FF# or else C1 >= 16#E000# then
            Result (Len + 1) :=
              Character'Val
                (2#1110_0000# or Shift_Right (C1, 12));
            Result (Len + 2) :=
              Character'Val
                (2#10_000000# or (Shift_Right (C1, 6) and 2#00_111111#));
            Result (Len + 3) :=
              Character'Val
                (2#10_000000# or (C1 and 2#00_111111#));
            Len := Len + 3;
 
         --  Codes in the range 16#10000# - 16#10FFFF#
         --    UTF-16: 110110zzzzyyyyyy 110111yyxxxxxxxx
         --    UTF-8:  11110zzz 10zzyyyy 10yyyyxx 10xxxxxx
         --    Note: zzzzz in the output is input zzzz + 1
 
         elsif C1 <= 2#110110_11_11111111# then
            if Iptr > Item'Last then
               Raise_Encoding_Error (Iptr - 1);
            else
               C2 := To_Unsigned_16 (Item (Iptr));
               Iptr := Iptr + 1;
            end if;
 
            if (C2 and 2#111111_00_00000000#) /= 2#110111_00_00000000# then
               Raise_Encoding_Error (Iptr - 1);
            end if;
 
            zzzzz    := (Shift_Right (C1, 6) and 2#1111#) + 1;
            yyyyyyyy := ((Shift_Left (C1, 2) and 2#111111_00#)
                            or
                         (Shift_Right (C2, 8) and 2#000000_11#));
            xxxxxxxx := C2 and 2#11111111#;
 
            Result (Len + 1) :=
              Character'Val
                (2#11110_000# or (Shift_Right (zzzzz, 2)));
            Result (Len + 2) :=
              Character'Val
                (2#10_000000# or Shift_Left (zzzzz and 2#11#, 4)
                              or Shift_Right (yyyyyyyy, 4));
            Result (Len + 3) :=
              Character'Val
                (2#10_000000# or Shift_Left (yyyyyyyy and 2#1111#, 4)
                              or Shift_Right (xxxxxxxx, 6));
            Result (Len + 4) :=
              Character'Val
                (2#10_000000# or (xxxxxxxx and 2#00_111111#));
            Len := Len + 4;
 
         --  Error if input in 16#DC00# - 16#DFFF# (2nd surrogate with no 1st)
 
         else
            Raise_Encoding_Error (Iptr - 2);
         end if;
      end loop;
 
      return Result (1 .. Len);
   end Convert;
 
end Ada.Strings.UTF_Encoding.Conversions;