src/com/ibm/icu/text/CharsetRecog_2022.java

/*
*******************************************************************************
* Copyright (C) 2005, International Business Machines Corporation and         *
* others. All Rights Reserved.                                                *
*******************************************************************************
*/
package com.ibm.icu.text;

/**
 *  class CharsetRecog_2022  part of the ICU charset detection imlementation.
 *                           This is a superclass for the individual detectors for
 *                           each of the detectable members of the ISO 2022 family
 *                           of encodings.
 * 
 *                           The separate classes are nested within this class.
 * 
 * @internal
 */
abstract class CharsetRecog_2022 extends CharsetRecognizer {

    
    /**
     * Matching function shared among the 2022 detectors JP, CN and KR
     * Counts up the number of legal an unrecognized escape sequences in
     * the sample of text, and computes a score based on the total number &
     * the proportion that fit the encoding.
     * 
     * 
     * @param text the byte buffer containing text to analyse
     * @param textLen  the size of the text in the byte.
     * @param escapeSequences the byte escape sequences to test for.
     * @return match quality, in the range of 0-100.
     */
    int   match(byte [] text, int textLen, byte [][] escapeSequences) {
        int     i, j;
        int     escN;
        int     hits   = 0;
        int     misses = 0;
        int     shifts = 0;
        int     quality;
        scanInput:
            for (i=0; i<textLen; i++) {
                if (text[i] == 0x1b) {
                    checkEscapes:
                        for (escN=0; escN<escapeSequences.length; escN++) {
                            byte [] seq = escapeSequences[escN];
                            
                            for (j=1; j<seq.length; j++) {
                                if (seq[j] != text[i+j])  {
                                    continue checkEscapes;
                                }                                   
                            }
                            
                            hits++; 
                            i += seq.length-1;
                            continue scanInput;
                        }
                
                        misses++;                  
                }
                
                if (text[i] == 0x0e || text[i] == 0x0f) {
                    // Shift in/out
                    shifts++;
                }
            }
        
        if (hits == 0) {
            return 0;
        }
        
        //
        // Initial quality is based on relative proportion of recongized vs.
        //   unrecognized escape sequences. 
        //   All good:  quality = 100;
        //   half or less good: quality = 0;
        //   linear inbetween.
        quality = (100*hits - 100*misses) / (hits + misses);
        
        // Back off quality if there were too few escape sequences seen.
        //   Include shifts in this computation, so that KR does not get penalized
        //   for having only a single Escape sequence, but many shifts.
        if (hits+shifts < 5) {
            quality -= (5-(hits+shifts))*10;
        }
        
        if (quality < 0) {
            quality = 0;
        }        
        return quality;
    }

    
 
    
    static class CharsetRecog_2022JP extends CharsetRecog_2022 {
        private byte [] [] escapeSequences = {
                {0x1b, 0x24, 0x28, 0x43},   // KS X 1001:1992
                {0x1b, 0x24, 0x28, 0x44},   // JIS X 212-1990
                {0x1b, 0x24, 0x40},         // JIS C 6226-1978
                {0x1b, 0x24, 0x41},         // GB 2312-80
                {0x1b, 0x24, 0x42},         // JIS X 208-1983
                {0x1b, 0x26, 0x40},         // JIS X 208 1990, 1997
                {0x1b, 0x28, 0x42},         // ASCII
                {0x1b, 0x28, 0x48},         // JIS-Roman
                {0x1b, 0x28, 0x49},         // Half-width katakana
                {0x1b, 0x28, 0x4a},         // JIS-Roman
                {0x1b, 0x2e, 0x41},         // ISO 8859-1
                {0x1b, 0x2e, 0x46}          // ISO 8859-7
                };
        
        String getName() {
            return "ISO-2022-JP";
        }
        
        int   match(CharsetDetector det) {
            return match(det.fInputBytes, det.fInputLen, escapeSequences);
        }
    }

    static class CharsetRecog_2022KR extends CharsetRecog_2022 {
        private byte [] [] escapeSequences = {
                {0x1b, 0x24, 0x29, 0x43}   
                 };
        
        String getName() {
            return "ISO-2022-KR";
        }
        
        int   match(CharsetDetector det) {
            return match(det.fInputBytes, det.fInputLen, escapeSequences);
        }
        
    }

    static class CharsetRecog_2022CN extends CharsetRecog_2022 {
        private byte [] [] escapeSequences = {
                {0x1b, 0x24, 0x29, 0x41},   // GB 2312-80
                {0x1b, 0x24, 0x29, 0x47},   // CNS 11643-1992 Plane 1
                {0x1b, 0x24, 0x2A, 0x48},   // CNS 11643-1992 Plane 2
                {0x1b, 0x24, 0x29, 0x45},   // ISO-IR-165
                {0x1b, 0x24, 0x2B, 0x49},   // CNS 11643-1992 Plane 3
                {0x1b, 0x24, 0x2B, 0x4A},   // CNS 11643-1992 Plane 4
                {0x1b, 0x24, 0x2B, 0x4B},   // CNS 11643-1992 Plane 5
                {0x1b, 0x24, 0x2B, 0x4C},   // CNS 11643-1992 Plane 6
                {0x1b, 0x24, 0x2B, 0x4D},   // CNS 11643-1992 Plane 7
                {0x1b, 0x4e},               // SS2
                {0x1b, 0x4f},               // SS3
        };
        
        String getName() {
            return "ISO-2022-CN";
        }
        
        
        int   match(CharsetDetector det) {
            return match(det.fInputBytes, det.fInputLen, escapeSequences);
        }
    }
    
    }