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/* $Id$
Part of SWI-Prolog
Author: Jan Wielemaker
E-mail: wielemak@science.uva.nl
WWW: http://www.swi-prolog.org
Copyright (C): 1985-2005, University of Amsterdam
This program 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 program 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 you link this library with other files,
compiled with a Free Software compiler, to produce an executable, this
library 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 General Public License.
*/
:- module(utf8,
[ utf8_codes//1 % ?String
]).
%% utf8_codes(?Codes)// is det.
%
% DCG translating between a Unicode code-list and its UTF-8
% encoded byte-string. The DCG works two ways. Encoding a
% code-list to a UTF-8 byte string is achieved using
%
% phrase(utf8_codes(Codes), UTF8)
%
% The algorithm is a close copy of the C-algorithm used
% internally and defined in src/pl-utf8.c
%
% NOTE: in many cases you can avoid this library and leave
% encoding and decoding to I/O streams. If only part of the data
% is to be encoded the encoding of a stream can be switched
% temporary using set_stream(Stream, encoding(utf8))
utf8_codes([H|T]) -->
utf8_code(H), !,
utf8_codes(T).
utf8_codes([]) -->
[].
utf8_code(C) -->
[C0],
{ nonvar(C0) }, !, % decoding version
( {C0 < 0x80}
-> {C = C0}
; {C0/\0xe0 =:= 0xc0}
-> utf8_cont(C1, 0),
{C is (C0/\0x1f)<<6\/C1}
; {C0/\0xf0 =:= 0xe0}
-> utf8_cont(C1, 6),
utf8_cont(C2, 0),
{C is ((C0/\0xf)<<12)\/C1\/C2}
; {C0/\0xf8 =:= 0xf0}
-> utf8_cont(C1, 12),
utf8_cont(C2, 6),
utf8_cont(C3, 0),
{C is ((C0/\0x7)<<18)\/C1\/C2\/C3}
; {C0/\0xfc =:= 0xf8}
-> utf8_cont(C1, 18),
utf8_cont(C2, 12),
utf8_cont(C3, 6),
utf8_cont(C4, 0),
{C is ((C0/\0x3)<<24)\/C1\/C2\/C3\/C4}
; {C0/\0xfe =:= 0xfc}
-> utf8_cont(C1, 24),
utf8_cont(C2, 18),
utf8_cont(C3, 12),
utf8_cont(C4, 6),
utf8_cont(C5, 0),
{C is ((C0/\0x1)<<30)\/C1\/C2\/C3\/C4\/C5}
).
utf8_code(C) -->
{ nonvar(C) }, !, % encoding version
( { C < 0x80 }
-> [C]
; { C < 0x800 }
-> { C0 is 0xc0\/((C>>6)/\0x1f),
C1 is 0x80\/(C/\0x3f)
},
[C0,C1]
; { C < 0x10000 }
-> { C0 is 0xe0\/((C>>12)/\0x0f),
C1 is 0x80\/((C>>6)/\0x3f),
C2 is 0x80\/(C/\0x3f)
},
[C0,C1,C2]
; { C < 0x200000 }
-> { C0 is 0xf0\/((C>>18)/\0x07),
C1 is 0x80\/((C>>12)/\0x3f),
C2 is 0x80\/((C>>6)/\0x3f),
C3 is 0x80\/(C/\0x3f)
},
[C0,C1,C2,C3]
; { C < 0x4000000 }
-> { C0 is 0xf8\/((C>>24)/\0x03),
C1 is 0x80\/((C>>18)/\0x3f),
C2 is 0x80\/((C>>12)/\0x3f),
C3 is 0x80\/((C>>6)/\0x3f),
C4 is 0x80\/(C/\0x3f)
},
[C0,C1,C2,C3,C4]
; { C < 0x80000000 }
-> { C0 is 0xfc\/((C>>30)/\0x01),
C1 is 0x80\/((C>>24)/\0x3f),
C2 is 0x80\/((C>>18)/\0x3f),
C3 is 0x80\/((C>>12)/\0x3f),
C4 is 0x80\/((C>>6)/\0x3f),
C5 is 0x80\/(C/\0x3f)
},
[C0,C1,C2,C3,C4,C5]
).
utf8_cont(Val, Shift) -->
[C],
{ C/\0xc0 =:= 0x80,
Val is (C/\0x3f)<<Shift
}.
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