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 /* -*- Mode: C; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */

 /* This Source Code Form is subject to the terms of the Mozilla Public

  * License, v. 2.0. If a copy of the MPL was not distributed with this

  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

 #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, uint32_t aLen);

   virtual const char* GetCharSetName();

   virtual void Reset(void);

   virtual nsProbingState GetState(void);

   virtual float     GetConfidence(void) { return (float)0.0; }

   void SetModelProbers(nsCharSetProber *logicalPrb, nsCharSetProber *visualPrb) 

   { mLogicalProb = logicalPrb; mVisualProb = visualPrb; }

 #ifdef DEBUG_chardet

   virtual void  DumpStatus();

 #endif

 protected:

   static bool isFinal(char c);

   static bool isNonFinal(char c);

   int32_t 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__ */