@nuintun/qrcode/cjs/common/image/utils/lzw/Dict.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 Dict
 * @see https://github.com/google/dart-gif-encoder
 */
// The highest code that can be defined in the CodeBook.
const MAX_CODE = (1 << 12) - 1;
/**
 * A dict contains codes defined during LZW compression. It's a mapping from a string
 * of pixels to the code that represents it. The codes are stored in a trie which is
 * represented as a map. Codes may be up to 12 bits. The size of the codebook is always
 * the minimum power of 2 needed to represent all the codes and automatically increases
 * as new codes are defined.
 */
class Dict {
  #bof;
  #eof;
  #bits;
  #depth;
  #size;
  #unused;
  #codes;
  constructor(depth) {
    const bof = 1 << depth;
    const eof = bof + 1;
    this.#bof = bof;
    this.#eof = eof;
    this.#depth = depth;
    this.reset();
  }
  get bof() {
    return this.#bof;
  }
  get eof() {
    return this.#eof;
  }
  get bits() {
    return this.#bits;
  }
  get depth() {
    return this.#depth;
  }
  reset() {
    const bits = this.#depth + 1;
    this.#bits = bits;
    this.#size = 1 << bits;
    this.#codes = new Map();
    this.#unused = this.#eof + 1;
  }
  add(code, index) {
    let unused = this.#unused;
    if (unused > MAX_CODE) {
      return false;
    }
    this.#codes.set((code << 8) | index, unused++);
    let bits = this.#bits;
    let size = this.#size;
    if (unused > size) {
      size = 1 << ++bits;
    }
    this.#bits = bits;
    this.#size = size;
    this.#unused = unused;
    return true;
  }
  get(code, index) {
    return this.#codes.get((code << 8) | index);
  }
}

exports.Dict = Dict;