src/sbcharsetprober.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 logger = require('./logger');

function SingleByteCharSetProber(model, reversed, nameProber) {
    CharSetProber.apply(this);

    var SAMPLE_SIZE = 64;
    var SB_ENOUGH_REL_THRESHOLD = 1024;
    var POSITIVE_SHORTCUT_THRESHOLD = 0.95;
    var NEGATIVE_SHORTCUT_THRESHOLD = 0.05;
    var SYMBOL_CAT_ORDER = 250;
    var NUMBER_OF_SEQ_CAT = 4;
    var POSITIVE_CAT = NUMBER_OF_SEQ_CAT - 1;
    //var NEGATIVE_CAT = 0;

    var self = this;

    function init(model, reversed, nameProber) {
        self._mModel = model;
        self._mReversed = reversed; // "true" if we need to reverse every pair in the model lookup
        self._mNameProber = nameProber; // Optional auxiliary prober for name decision
        self.reset();
    }

    this.reset = function() {
        SingleByteCharSetProber.prototype.reset.apply(this);
        this._mLastOrder = 255; // char order of last character
        this._mSeqCounters = [];
        for( var i = 0; i < NUMBER_OF_SEQ_CAT; this._mSeqCounters[i++] = 0 );
        this._mTotalSeqs = 0;
        this._mTotalChar = 0;
        this._mFreqChar = 0; // characters that fall in our sampling range
    }

    this.getCharsetName = function() {
        if( this._mNameProber ) {
            return this._mNameProber.getCharsetName();
        } else {
            return this._mModel.charsetName;
        }
    }

    this.feed = function(aBuf) {
        if( ! this._mModel.keepEnglishLetter ) {
            aBuf = this.filterWithoutEnglishLetters(aBuf);
        }
        var aLen = aBuf.length;
        if( !aLen ) {
            return this.getState();
        }
        for( var i = 0, c; i < aLen; i++ )
        {
            c = aBuf.charCodeAt(i);
            var order = this._mModel.charToOrderMap[c];
            if( order < SYMBOL_CAT_ORDER ) {
                this._mTotalChar++;
            }
            if( order < SAMPLE_SIZE ) {
                this._mFreqChar++;
                if( this._mLastOrder < SAMPLE_SIZE ) {
                    this._mTotalSeqs++;
                    if( !this._mReversed ) {
                        this._mSeqCounters[this._mModel.precedenceMatrix[(this._mLastOrder * SAMPLE_SIZE) + order]]++;
                    } else { // reverse the order of the letters in the lookup
                        this._mSeqCounters[this._mModel.precedenceMatrix[(order * SAMPLE_SIZE) + this._mLastOrder]]++;
                    }
                }
            }
            this._mLastOrder = order;
        }

        if( this.getState() == constants.detecting ) {
            if( self._mTotalSeqs > SB_ENOUGH_REL_THRESHOLD ) {
                var cf = this.getConfidence();
                if( cf > POSITIVE_SHORTCUT_THRESHOLD ) {
                    logger.log(this._mModel.charsetName + " confidence = " + cf + ", we have a winner\n");
                } else if( cf < NEGATIVE_SHORTCUT_THRESHOLD ) {
                    logger.log(this._mModel.charsetName + " confidence = " + cf + ", below negative shortcut threshhold " + NEGATIVE_SHORTCUT_THRESHOLD + "\n");
                    this._mState = constants.notMe;
                }
            }
        }

        return this.getState();
    }

    this.getConfidence = function() {
        var r = 0.01;
        if( this._mTotalSeqs > 0 ) {
            //logger.log(this._mSeqCounters[POSITIVE_CAT] + " " + this._mTotalSeqs + " " + this._mModel.mTypicalPositiveRatio);
            r = (1.0 * this._mSeqCounters[POSITIVE_CAT]) / this._mTotalSeqs / this._mModel.mTypicalPositiveRatio;
            //logger.log(r + " " + this._mFreqChar + " " + this._mTotalChar);
            r *= this._mFreqChar / this._mTotalChar;
            if( r >= 1.0 ) {
                r = 0.99;
            }
        }
        return r;
    }

    reversed = reversed !== undefined ? reversed : false;
    nameProber = nameProber !== undefined ? nameProber : null;
    init(model, reversed, nameProber);
}
SingleByteCharSetProber.prototype = new CharSetProber();

module.exports = SingleByteCharSetProber