src/latin1prober.js

/*
 * The Original Code is Mozilla Universal charset detector code.
 *
 * The Initial Developer of the Original Code is
 * Netscape Communications Corporation.
 * Portions created by the Initial Developer are Copyright (C) 2001
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   António Afonso (antonio.afonso gmail.com) - port to JavaScript
 *   Mark Pilgrim - port to Python
 *   Shy Shalom - original C code
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
 * 02110-1301  USA
 */

var CharSetProber = require('./charsetprober');
var Constants = require('./constants');

var UDF = 0; // undefined
var OTH = 1; // other
var ASC = 2; // ascii capital letter
var ASS = 3; // ascii small letter
var ACV = 4; // accent capital vowel
var ACO = 5; // accent capital other
var ASV = 6; // accent small vowel
var ASO = 7; // accent small other

var Latin1_CharToClass = [
  OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   // 00 - 07
  OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   // 08 - 0F
  OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   // 10 - 17
  OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   // 18 - 1F
  OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   // 20 - 27
  OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   // 28 - 2F
  OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   // 30 - 37
  OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   // 38 - 3F
  OTH, ASC, ASC, ASC, ASC, ASC, ASC, ASC,   // 40 - 47
  ASC, ASC, ASC, ASC, ASC, ASC, ASC, ASC,   // 48 - 4F
  ASC, ASC, ASC, ASC, ASC, ASC, ASC, ASC,   // 50 - 57
  ASC, ASC, ASC, OTH, OTH, OTH, OTH, OTH,   // 58 - 5F
  OTH, ASS, ASS, ASS, ASS, ASS, ASS, ASS,   // 60 - 67
  ASS, ASS, ASS, ASS, ASS, ASS, ASS, ASS,   // 68 - 6F
  ASS, ASS, ASS, ASS, ASS, ASS, ASS, ASS,   // 70 - 77
  ASS, ASS, ASS, OTH, OTH, OTH, OTH, OTH,   // 78 - 7F
  OTH, UDF, OTH, ASO, OTH, OTH, OTH, OTH,   // 80 - 87
  OTH, OTH, ACO, OTH, ACO, UDF, ACO, UDF,   // 88 - 8F
  UDF, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   // 90 - 97
  OTH, OTH, ASO, OTH, ASO, UDF, ASO, ACO,   // 98 - 9F
  OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   // A0 - A7
  OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   // A8 - AF
  OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   // B0 - B7
  OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   // B8 - BF
  ACV, ACV, ACV, ACV, ACV, ACV, ACO, ACO,   // C0 - C7
  ACV, ACV, ACV, ACV, ACV, ACV, ACV, ACV,   // C8 - CF
  ACO, ACO, ACV, ACV, ACV, ACV, ACV, OTH,   // D0 - D7
  ACV, ACV, ACV, ACV, ACV, ACO, ACO, ACO,   // D8 - DF
  ASV, ASV, ASV, ASV, ASV, ASV, ASO, ASO,   // E0 - E7
  ASV, ASV, ASV, ASV, ASV, ASV, ASV, ASV,   // E8 - EF
  ASO, ASO, ASV, ASV, ASV, ASV, ASV, OTH,   // F0 - F7
  ASV, ASV, ASV, ASV, ASV, ASO, ASO, ASO    // F8 - FF
];

// 0 : illegal
// 1 : very unlikely
// 2 : normal
// 3 : very likely
var Latin1ClassModel = [
// UDF OTH ASC ASS ACV ACO ASV ASO
   0,  0,  0,  0,  0,  0,  0,  0,  // UDF
   0,  3,  3,  3,  3,  3,  3,  3,  // OTH
   0,  3,  3,  3,  3,  3,  3,  3,  // ASC
   0,  3,  3,  3,  1,  1,  3,  3,  // ASS
   0,  3,  3,  3,  1,  2,  1,  2,  // ACV
   0,  3,  3,  3,  3,  3,  3,  3,  // ACO
   0,  3,  1,  3,  1,  1,  1,  3,  // ASV
   0,  3,  1,  3,  1,  1,  3,  3   // ASO
];

function Latin1Prober() {
    CharSetProber.apply(this);

    var FREQ_CAT_NUM = 4;
    var CLASS_NUM = 8; // total classes
    var self = this;

    function init() {
        self.reset();
    }

    this.reset = function() {
        this._mLastCharClass = OTH;
        this._mFreqCounter = [];
        for( var i = 0; i < FREQ_CAT_NUM; this._mFreqCounter[i++] = 0 );
        Latin1Prober.prototype.reset.apply(this);
    }

    this.getCharsetName = function() {
        return "windows-1252";
    }

    this.getSupportedCharsetNames = function() {
        return [this.getCharsetName()];
    }

    this.feed = function (aBuf) {
        aBuf = this.removeXmlTags(aBuf);
        for( var i = 0; i < aBuf.length; i++ ) {
            var c = aBuf.charCodeAt(i);
            var charClass = Latin1_CharToClass[c];
            var freq = Latin1ClassModel[(this._mLastCharClass * CLASS_NUM) + charClass];
            if( freq == 0 ) {
                this._mState = Constants.notMe;
                break;
            }
            this._mFreqCounter[freq]++;
            this._mLastCharClass = charClass;
        }

        return this.getState();
    }

    this.getConfidence = function() {
        var confidence;

        if( this.getState() == Constants.notMe ) {
            return 0.01;
        }

        var total = 0;
        for( var i = 0; i < this._mFreqCounter.length; i++ ) {
            total += this._mFreqCounter[i];
        }
        if( total < 0.01 ) {
            confidence = 0.0;
        } else {
            confidence = (this._mFreqCounter[3] / total) - (this._mFreqCounter[1] * 20 / total);
        }
        if( confidence < 0 ) {
            confidence = 0.0;
        }
        // lower the confidence of latin1 so that other more accurate detector
        // can take priority.
        //
        // antonio.afonso: need to change this otherwise languages like pt, es, fr using latin1 will never be detected.
        confidence = confidence * 0.95;
        return confidence;
    }

    init();
}
Latin1Prober.prototype = new CharSetProber();

module.exports = Latin1Prober