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2 : /* ***** BEGIN LICENSE BLOCK *****
3 : * Version: MPL 1.1/GPL 2.0/LGPL 2.1
4 : *
5 : * The contents of this file are subject to the Mozilla Public License Version
6 : * 1.1 (the "License"); you may not use this file except in compliance with
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10 : * Software distributed under the License is distributed on an "AS IS" basis,
11 : * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
12 : * for the specific language governing rights and limitations under the
13 : * License.
14 : *
15 : * The Original Code is Mozilla Universal charset detector code.
16 : *
17 : * The Initial Developer of the Original Code is
18 : * Shy Shalom <shooshX@gmail.com>
19 : * Portions created by the Initial Developer are Copyright (C) 2005
20 : * the Initial Developer: All Rights Reserved.
21 : *
22 : * Contributor(s):
23 : *
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36 : * ***** END LICENSE BLOCK ***** */
37 :
38 : #ifndef nsHebrewProber_h__
39 : #define nsHebrewProber_h__
40 :
41 : #include "nsSBCharSetProber.h"
42 :
43 : // This prober doesn't actually recognize a language or a charset.
44 : // It is a helper prober for the use of the Hebrew model probers
45 : class nsHebrewProber: public nsCharSetProber
46 : {
47 : public:
48 0 : nsHebrewProber(void) :mLogicalProb(0), mVisualProb(0) { Reset(); }
49 :
50 0 : virtual ~nsHebrewProber(void) {}
51 : virtual nsProbingState HandleData(const char* aBuf, PRUint32 aLen);
52 : virtual const char* GetCharSetName();
53 : virtual void Reset(void);
54 :
55 : virtual nsProbingState GetState(void);
56 :
57 0 : virtual float GetConfidence(void) { return (float)0.0; }
58 0 : virtual void SetOpion() {}
59 :
60 0 : void SetModelProbers(nsCharSetProber *logicalPrb, nsCharSetProber *visualPrb)
61 0 : { mLogicalProb = logicalPrb; mVisualProb = visualPrb; }
62 :
63 : #ifdef DEBUG_chardet
64 : virtual void DumpStatus();
65 : #endif
66 :
67 : protected:
68 : static bool isFinal(char c);
69 : static bool isNonFinal(char c);
70 :
71 : PRInt32 mFinalCharLogicalScore, mFinalCharVisualScore;
72 :
73 : // The two last characters seen in the previous buffer.
74 : char mPrev, mBeforePrev;
75 :
76 : // These probers are owned by the group prober.
77 : nsCharSetProber *mLogicalProb, *mVisualProb;
78 : };
79 :
80 : /**
81 : * ** General ideas of the Hebrew charset recognition **
82 : *
83 : * Four main charsets exist in Hebrew:
84 : * "ISO-8859-8" - Visual Hebrew
85 : * "windows-1255" - Logical Hebrew
86 : * "ISO-8859-8-I" - Logical Hebrew
87 : * "x-mac-hebrew" - ?? Logical Hebrew ??
88 : *
89 : * Both "ISO" charsets use a completely identical set of code points, whereas
90 : * "windows-1255" and "x-mac-hebrew" are two different proper supersets of
91 : * these code points. windows-1255 defines additional characters in the range
92 : * 0x80-0x9F as some misc punctuation marks as well as some Hebrew-specific
93 : * diacritics and additional 'Yiddish' ligature letters in the range 0xc0-0xd6.
94 : * x-mac-hebrew defines similar additional code points but with a different
95 : * mapping.
96 : *
97 : * As far as an average Hebrew text with no diacritics is concerned, all four
98 : * charsets are identical with respect to code points. Meaning that for the
99 : * main Hebrew alphabet, all four map the same values to all 27 Hebrew letters
100 : * (including final letters).
101 : *
102 : * The dominant difference between these charsets is their directionality.
103 : * "Visual" directionality means that the text is ordered as if the renderer is
104 : * not aware of a BIDI rendering algorithm. The renderer sees the text and
105 : * draws it from left to right. The text itself when ordered naturally is read
106 : * backwards. A buffer of Visual Hebrew generally looks like so:
107 : * "[last word of first line spelled backwards] [whole line ordered backwards
108 : * and spelled backwards] [first word of first line spelled backwards]
109 : * [end of line] [last word of second line] ... etc' "
110 : * adding punctuation marks, numbers and English text to visual text is
111 : * naturally also "visual" and from left to right.
112 : *
113 : * "Logical" directionality means the text is ordered "naturally" according to
114 : * the order it is read. It is the responsibility of the renderer to display
115 : * the text from right to left. A BIDI algorithm is used to place general
116 : * punctuation marks, numbers and English text in the text.
117 : *
118 : * Texts in x-mac-hebrew are almost impossible to find on the Internet. From
119 : * what little evidence I could find, it seems that its general directionality
120 : * is Logical.
121 : *
122 : * To sum up all of the above, the Hebrew probing mechanism knows about two
123 : * charsets:
124 : * Visual Hebrew - "ISO-8859-8" - backwards text - Words and sentences are
125 : * backwards while line order is natural. For charset recognition purposes
126 : * the line order is unimportant (In fact, for this implementation, even
127 : * word order is unimportant).
128 : * Logical Hebrew - "windows-1255" - normal, naturally ordered text.
129 : *
130 : * "ISO-8859-8-I" is a subset of windows-1255 and doesn't need to be
131 : * specifically identified.
132 : * "x-mac-hebrew" is also identified as windows-1255. A text in x-mac-hebrew
133 : * that contain special punctuation marks or diacritics is displayed with
134 : * some unconverted characters showing as question marks. This problem might
135 : * be corrected using another model prober for x-mac-hebrew. Due to the fact
136 : * that x-mac-hebrew texts are so rare, writing another model prober isn't
137 : * worth the effort and performance hit.
138 : *
139 : * *** The Prober ***
140 : *
141 : * The prober is divided between two nsSBCharSetProbers and an nsHebrewProber,
142 : * all of which are managed, created, fed data, inquired and deleted by the
143 : * nsSBCSGroupProber. The two nsSBCharSetProbers identify that the text is in
144 : * fact some kind of Hebrew, Logical or Visual. The final decision about which
145 : * one is it is made by the nsHebrewProber by combining final-letter scores
146 : * with the scores of the two nsSBCharSetProbers to produce a final answer.
147 : *
148 : * The nsSBCSGroupProber is responsible for stripping the original text of HTML
149 : * tags, English characters, numbers, low-ASCII punctuation characters, spaces
150 : * and new lines. It reduces any sequence of such characters to a single space.
151 : * The buffer fed to each prober in the SBCS group prober is pure text in
152 : * high-ASCII.
153 : * The two nsSBCharSetProbers (model probers) share the same language model:
154 : * Win1255Model.
155 : * The first nsSBCharSetProber uses the model normally as any other
156 : * nsSBCharSetProber does, to recognize windows-1255, upon which this model was
157 : * built. The second nsSBCharSetProber is told to make the pair-of-letter
158 : * lookup in the language model backwards. This in practice exactly simulates
159 : * a visual Hebrew model using the windows-1255 logical Hebrew model.
160 : *
161 : * The nsHebrewProber is not using any language model. All it does is look for
162 : * final-letter evidence suggesting the text is either logical Hebrew or visual
163 : * Hebrew. Disjointed from the model probers, the results of the nsHebrewProber
164 : * alone are meaningless. nsHebrewProber always returns 0.00 as confidence
165 : * since it never identifies a charset by itself. Instead, the pointer to the
166 : * nsHebrewProber is passed to the model probers as a helper "Name Prober".
167 : * When the Group prober receives a positive identification from any prober,
168 : * it asks for the name of the charset identified. If the prober queried is a
169 : * Hebrew model prober, the model prober forwards the call to the
170 : * nsHebrewProber to make the final decision. In the nsHebrewProber, the
171 : * decision is made according to the final-letters scores maintained and Both
172 : * model probers scores. The answer is returned in the form of the name of the
173 : * charset identified, either "windows-1255" or "ISO-8859-8".
174 : *
175 : */
176 : #endif /* nsHebrewProber_h__ */
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