@nuintun/qrcode/cjs/common/BitSource.cjs

A pure JavaScript QRCode encode and decode library.

/**
 * @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
 */

'use strict';

/**
 * @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;
  }
}

exports.BitSource = BitSource;