@zxing/text-encoding
Version:
Polyfill for the Encoding Living Standard's API.
142 lines • 6.64 kB
JavaScript
import { decoderError } from "../../encoding/encodings";
import { finished } from "../../encoding/finished";
import { index, indexCodePointFor, indexGB18030RangesCodePointFor } from "../../encoding/indexes";
import { end_of_stream, isASCIIByte } from "../../encoding/terminology";
import { inRange } from "../../encoding/utilities";
/**
* @constructor
* @implements {Decoder}
* @param {{fatal: boolean}} options
*/
export class GB18030Decoder {
constructor(options) {
this.fatal = options.fatal;
// gb18030's decoder has an associated gb18030 first, gb18030
// second, and gb18030 third (all initially 0x00).
/** @type {number} */ this.gb18030_first = 0x00,
/** @type {number} */ this.gb18030_second = 0x00,
/** @type {number} */ this.gb18030_third = 0x00;
}
/**
* @param {Stream} stream The stream of bytes being decoded.
* @param {number} bite The next byte read from the stream.
* @return {?(number|!Array.<number>)} The next code point(s)
* decoded, or null if not enough data exists in the input
* stream to decode a complete code point.
*/
handler(stream, bite) {
// 1. If byte is end-of-stream and gb18030 first, gb18030
// second, and gb18030 third are 0x00, return finished.
if (bite === end_of_stream && this.gb18030_first === 0x00 &&
this.gb18030_second === 0x00 && this.gb18030_third === 0x00) {
return finished;
}
// 2. If byte is end-of-stream, and gb18030 first, gb18030
// second, or gb18030 third is not 0x00, set gb18030 first,
// gb18030 second, and gb18030 third to 0x00, and return error.
if (bite === end_of_stream &&
(this.gb18030_first !== 0x00 || this.gb18030_second !== 0x00 ||
this.gb18030_third !== 0x00)) {
this.gb18030_first = 0x00;
this.gb18030_second = 0x00;
this.gb18030_third = 0x00;
decoderError(this.fatal);
}
let code_point;
// 3. If gb18030 third is not 0x00, run these substeps:
if (this.gb18030_third !== 0x00) {
// 1. Let code point be null.
code_point = null;
// 2. If byte is in the range 0x30 to 0x39, inclusive, set
// code point to the index gb18030 ranges code point for
// (((gb18030 first − 0x81) × 10 + gb18030 second − 0x30) ×
// 126 + gb18030 third − 0x81) × 10 + byte − 0x30.
if (inRange(bite, 0x30, 0x39)) {
code_point = indexGB18030RangesCodePointFor((((this.gb18030_first - 0x81) * 10 + this.gb18030_second - 0x30) * 126 +
this.gb18030_third - 0x81) * 10 + bite - 0x30);
}
// 3. Let buffer be a byte sequence consisting of gb18030
// second, gb18030 third, and byte, in order.
const buffer = [this.gb18030_second, this.gb18030_third, bite];
// 4. Set gb18030 first, gb18030 second, and gb18030 third to
// 0x00.
this.gb18030_first = 0x00;
this.gb18030_second = 0x00;
this.gb18030_third = 0x00;
// 5. If code point is null, prepend buffer to stream and
// return error.
if (code_point === null) {
stream.prepend(buffer);
return decoderError(this.fatal);
}
// 6. Return a code point whose value is code point.
return code_point;
}
// 4. If gb18030 second is not 0x00, run these substeps:
if (this.gb18030_second !== 0x00) {
// 1. If byte is in the range 0x81 to 0xFE, inclusive, set
// gb18030 third to byte and return continue.
if (inRange(bite, 0x81, 0xFE)) {
this.gb18030_third = bite;
return null;
}
// 2. Prepend gb18030 second followed by byte to stream, set
// gb18030 first and gb18030 second to 0x00, and return error.
stream.prepend([this.gb18030_second, bite]);
this.gb18030_first = 0x00;
this.gb18030_second = 0x00;
return decoderError(this.fatal);
}
// 5. If gb18030 first is not 0x00, run these substeps:
if (this.gb18030_first !== 0x00) {
// 1. If byte is in the range 0x30 to 0x39, inclusive, set
// gb18030 second to byte and return continue.
if (inRange(bite, 0x30, 0x39)) {
this.gb18030_second = bite;
return null;
}
// 2. Let lead be gb18030 first, let pointer be null, and set
// gb18030 first to 0x00.
const lead = this.gb18030_first;
let pointer = null;
this.gb18030_first = 0x00;
// 3. Let offset be 0x40 if byte is less than 0x7F and 0x41
// otherwise.
const offset = bite < 0x7F ? 0x40 : 0x41;
// 4. If byte is in the range 0x40 to 0x7E, inclusive, or 0x80
// to 0xFE, inclusive, set pointer to (lead − 0x81) × 190 +
// (byte − offset).
if (inRange(bite, 0x40, 0x7E) || inRange(bite, 0x80, 0xFE))
pointer = (lead - 0x81) * 190 + (bite - offset);
// 5. Let code point be null if pointer is null and the index
// code point for pointer in index gb18030 otherwise.
code_point = pointer === null ? null :
indexCodePointFor(pointer, index('gb18030'));
// 6. If code point is null and byte is an ASCII byte, prepend
// byte to stream.
if (code_point === null && isASCIIByte(bite))
stream.prepend(bite);
// 7. If code point is null, return error.
if (code_point === null)
return decoderError(this.fatal);
// 8. Return a code point whose value is code point.
return code_point;
}
// 6. If byte is an ASCII byte, return a code point whose value
// is byte.
if (isASCIIByte(bite))
return bite;
// 7. If byte is 0x80, return code point U+20AC.
if (bite === 0x80)
return 0x20AC;
// 8. If byte is in the range 0x81 to 0xFE, inclusive, set
// gb18030 first to byte and return continue.
if (inRange(bite, 0x81, 0xFE)) {
this.gb18030_first = bite;
return null;
}
// 9. Return error.
return decoderError(this.fatal);
}
}
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