chardet/src/encoding/iso2022.ts

132 lines
3.7 KiB
TypeScript
Raw Normal View History

import { Context, Recogniser } from '.';
2020-09-23 03:06:43 +00:00
import match, { Match } from '../match'
/**
* This is a superclass for the individual detectors for
* each of the detectable members of the ISO 2022 family
* of encodings.
*/
class ISO_2022 implements Recogniser {
escapeSequences: number[][] = [];
name() {
return 'ISO_2022';
}
2020-09-23 03:06:43 +00:00
match(det: Context): Match | null {
/**
* 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.
*/
2020-09-23 02:16:38 +00:00
let i, j;
let escN;
let hits = 0;
let misses = 0;
let shifts = 0;
let quality;
// TODO: refactor me
2020-09-23 02:16:38 +00:00
const text = det.fInputBytes;
const textLen = det.fInputLen;
scanInput: for (i = 0; i < textLen; i++) {
if (text[i] == 0x1b) {
checkEscapes: for (
escN = 0;
escN < this.escapeSequences.length;
escN++
) {
2020-09-23 02:16:38 +00:00
const seq = this.escapeSequences[escN];
if (textLen - i < seq.length) continue checkEscapes;
for (j = 1; j < seq.length; j++)
if (seq[j] != text[i + j]) continue checkEscapes;
hits++;
i += seq.length - 1;
continue scanInput;
}
misses++;
}
// Shift in/out
if (text[i] == 0x0e || text[i] == 0x0f) shifts++;
}
if (hits == 0) return null;
//
// Initial quality is based on relative proportion of recognized vs.
// unrecognized escape sequences.
// All good: quality = 100;
// half or less good: quality = 0;
// linear in between.
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;
return quality <= 0 ? null : match(det, this, quality);
}
}
export class ISO_2022_JP extends ISO_2022 {
name() {
return 'ISO-2022-JP';
}
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
];
}
export class ISO_2022_KR extends ISO_2022 {
name() {
return 'ISO-2022-KR';
}
escapeSequences = [[0x1b, 0x24, 0x29, 0x43]];
}
export class ISO_2022_CN extends ISO_2022 {
name() {
return 'ISO-2022-CN';
}
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
];
}