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Diffstat (limited to 'src/ext/libcharsetdetect/mozilla/extensions/universalchardet/src/base/nsHebrewProber.h')
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1 files changed, 176 insertions, 0 deletions
diff --git a/src/ext/libcharsetdetect/mozilla/extensions/universalchardet/src/base/nsHebrewProber.h b/src/ext/libcharsetdetect/mozilla/extensions/universalchardet/src/base/nsHebrewProber.h new file mode 100644 index 0000000..eedfed4 --- /dev/null +++ b/src/ext/libcharsetdetect/mozilla/extensions/universalchardet/src/base/nsHebrewProber.h @@ -0,0 +1,176 @@ +/* -*- 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 + * of those above. If you wish to allow use of your version of this file only + * under the terms of either the GPL or the LGPL, and not to allow others to + * use your version of this file under the terms of the MPL, indicate your + * decision by deleting the provisions above and replace them with the notice + * and other provisions required by the GPL or the LGPL. If you do not delete + * the provisions above, a recipient may use your version of this file under + * the terms of any one of the MPL, the GPL or the LGPL. + * + * ***** 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__ */ |