@nuintun/qrcode
Version:
A pure JavaScript QRCode encode and decode library.
72 lines (69 loc) • 1.82 kB
JavaScript
/**
* @module QRCode
* @package @nuintun/qrcode
* @license MIT
* @version 5.0.2
* @author nuintun <nuintun@qq.com>
* @description A pure JavaScript QRCode encode and decode library.
* @see https://github.com/nuintun/qrcode#readme
*/
/**
* @module BitSource
*/
class BitSource {
#bytes;
#bitOffset;
#byteOffset;
constructor(bytes) {
this.#bytes = bytes;
this.#bitOffset = 0;
this.#byteOffset = 0;
}
get bitOffset() {
return this.#bitOffset;
}
get byteOffset() {
return this.#byteOffset;
}
read(length) {
let result = 0;
let bitOffset = this.#bitOffset;
let byteOffset = this.#byteOffset;
const bytes = this.#bytes;
// First, read remainder from current byte.
if (bitOffset > 0) {
const bitsLeft = 8 - bitOffset;
const toRead = Math.min(length, bitsLeft);
const bitsToNotRead = bitsLeft - toRead;
const mask = (0xff >> (8 - toRead)) << bitsToNotRead;
length -= toRead;
bitOffset += toRead;
result = (bytes[byteOffset] & mask) >> bitsToNotRead;
if (bitOffset === 8) {
byteOffset++;
bitOffset = 0;
}
}
// Next read whole bytes.
if (length > 0) {
while (length >= 8) {
length -= 8;
result = (result << 8) | (bytes[byteOffset++] & 0xff);
}
// Finally read a partial byte.
if (length > 0) {
const bitsToNotRead = 8 - length;
const mask = (0xff >> bitsToNotRead) << bitsToNotRead;
bitOffset += length;
result = (result << length) | ((bytes[byteOffset] & mask) >> bitsToNotRead);
}
}
this.#bitOffset = bitOffset;
this.#byteOffset = byteOffset;
return result;
}
available() {
return 8 * (this.#bytes.length - this.#byteOffset) - this.#bitOffset;
}
}
export { BitSource };