/* -*- Mode: C; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* ***** BEGIN LICENSE BLOCK *****
* Version: MPL 1.1/GPL 2.0/LGPL 2.1
*
* The contents of this file are subject to the Mozilla Public License Version
* 1.1 (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
* http://www.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
* for the specific language governing rights and limitations under the
* License.
*
* The Original Code is Mozilla Universal charset detector code.
*
* The Initial Developer of the Original Code is
* Shy Shalom <shooshX@gmail.com>
* Portions created by the Initial Developer are Copyright (C) 2005
* the Initial Developer: All Rights Reserved.
*
* Contributor(s):
*
* Alternatively, the contents of this file may be used under the terms of
* either the GNU General Public License Version 2 or later (the "GPL"), or
* the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
* in which case the provisions of the GPL or the LGPL are applicable instead
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* ***** END LICENSE BLOCK ***** */
#ifndef nsHebrewProber_h__
#define nsHebrewProber_h__
#include "nsSBCharSetProber.h"
// This prober doesn't actually recognize a language or a charset.
// It is a helper prober for the use of the Hebrew model probers
class nsHebrewProber: public nsCharSetProber
{
public:
nsHebrewProber(void) :mLogicalProb(0), mVisualProb(0) { Reset(); }
virtual ~nsHebrewProber(void) {}
virtual nsProbingState HandleData(const char* aBuf, PRUint32 aLen);
virtual const char* GetCharSetName();
virtual void Reset(void);
virtual nsProbingState GetState(void);
virtual float GetConfidence(void) { return (float)0.0; }
virtual void SetOpion() {};
void SetModelProbers(nsCharSetProber *logicalPrb, nsCharSetProber *visualPrb)
{ mLogicalProb = logicalPrb; mVisualProb = visualPrb; }
#ifdef DEBUG_chardet
virtual void DumpStatus();
#endif
protected:
static PRBool isFinal(char c);
static PRBool isNonFinal(char c);
PRInt32 mFinalCharLogicalScore, mFinalCharVisualScore;
// The two last characters seen in the previous buffer.
char mPrev, mBeforePrev;
// These probers are owned by the group prober.
nsCharSetProber *mLogicalProb, *mVisualProb;
};
/**
* ** General ideas of the Hebrew charset recognition **
*
* Four main charsets exist in Hebrew:
* "ISO-8859-8" - Visual Hebrew
* "windows-1255" - Logical Hebrew
* "ISO-8859-8-I" - Logical Hebrew
* "x-mac-hebrew" - ?? Logical Hebrew ??
*
* Both "ISO" charsets use a completely identical set of code points, whereas
* "windows-1255" and "x-mac-hebrew" are two different proper supersets of
* these code points. windows-1255 defines additional characters in the range
* 0x80-0x9F as some misc punctuation marks as well as some Hebrew-specific
* diacritics and additional 'Yiddish' ligature letters in the range 0xc0-0xd6.
* x-mac-hebrew defines similar additional code points but with a different
* mapping.
*
* As far as an average Hebrew text with no diacritics is concerned, all four
* charsets are identical with respect to code points. Meaning that for the
* main Hebrew alphabet, all four map the same values to all 27 Hebrew letters
* (including final letters).
*
* The dominant difference between these charsets is their directionality.
* "Visual" directionality means that the text is ordered as if the renderer is
* not aware of a BIDI rendering algorithm. The renderer sees the text and
* draws it from left to right. The text itself when ordered naturally is read
* backwards. A buffer of Visual Hebrew generally looks like so:
* "[last word of first line spelled backwards] [whole line ordered backwards
* and spelled backwards] [first word of first line spelled backwards]
* [end of line] [last word of second line] ... etc' "
* adding punctuation marks, numbers and English text to visual text is
* naturally also "visual" and from left to right.
*
* "Logical" directionality means the text is ordered "naturally" according to
* the order it is read. It is the responsibility of the renderer to display
* the text from right to left. A BIDI algorithm is used to place general
* punctuation marks, numbers and English text in the text.
*
* Texts in x-mac-hebrew are almost impossible to find on the Internet. From
* what little evidence I could find, it seems that its general directionality
* is Logical.
*
* To sum up all of the above, the Hebrew probing mechanism knows about two
* charsets:
* Visual Hebrew - "ISO-8859-8" - backwards text - Words and sentences are
* backwards while line order is natural. For charset recognition purposes
* the line order is unimportant (In fact, for this implementation, even
* word order is unimportant).
* Logical Hebrew - "windows-1255" - normal, naturally ordered text.
*
* "ISO-8859-8-I" is a subset of windows-1255 and doesn't need to be
* specifically identified.
* "x-mac-hebrew" is also identified as windows-1255. A text in x-mac-hebrew
* that contain special punctuation marks or diacritics is displayed with
* some unconverted characters showing as question marks. This problem might
* be corrected using another model prober for x-mac-hebrew. Due to the fact
* that x-mac-hebrew texts are so rare, writing another model prober isn't
* worth the effort and performance hit.
*
* *** The Prober ***
*
* The prober is divided between two nsSBCharSetProbers and an nsHebrewProber,
* all of which are managed, created, fed data, inquired and deleted by the
* nsSBCSGroupProber. The two nsSBCharSetProbers identify that the text is in
* fact some kind of Hebrew, Logical or Visual. The final decision about which
* one is it is made by the nsHebrewProber by combining final-letter scores
* with the scores of the two nsSBCharSetProbers to produce a final answer.
*
* The nsSBCSGroupProber is responsible for stripping the original text of HTML
* tags, English characters, numbers, low-ASCII punctuation characters, spaces
* and new lines. It reduces any sequence of such characters to a single space.
* The buffer fed to each prober in the SBCS group prober is pure text in
* high-ASCII.
* The two nsSBCharSetProbers (model probers) share the same language model:
* Win1255Model.
* The first nsSBCharSetProber uses the model normally as any other
* nsSBCharSetProber does, to recognize windows-1255, upon which this model was
* built. The second nsSBCharSetProber is told to make the pair-of-letter
* lookup in the language model backwards. This in practice exactly simulates
* a visual Hebrew model using the windows-1255 logical Hebrew model.
*
* The nsHebrewProber is not using any language model. All it does is look for
* final-letter evidence suggesting the text is either logical Hebrew or visual
* Hebrew. Disjointed from the model probers, the results of the nsHebrewProber
* alone are meaningless. nsHebrewProber always returns 0.00 as confidence
* since it never identifies a charset by itself. Instead, the pointer to the
* nsHebrewProber is passed to the model probers as a helper "Name Prober".
* When the Group prober receives a positive identification from any prober,
* it asks for the name of the charset identified. If the prober queried is a
* Hebrew model prober, the model prober forwards the call to the
* nsHebrewProber to make the final decision. In the nsHebrewProber, the
* decision is made according to the final-letters scores maintained and Both
* model probers scores. The answer is returned in the form of the name of the
* charset identified, either "windows-1255" or "ISO-8859-8".
*
*/
#endif /* nsHebrewProber_h__ */