JavaScript: BitArray

bitarray.js

import { inflateRaw, deflateRaw } from "pako";

// https://en.wikipedia.org/wiki/Run-length_encoding
const Z_RLE = 3;

class BitArray {
  constructor(bitSize) {
    const remainder = Math.min(1, bitSize % 8);
    const byteSize = Math.floor(bitSize / 8) + remainder;
    const buffer = new ArrayBuffer(byteSize);
    this._arr = new Uint8Array(buffer);
    this._bitSize = bitSize;
  }

  *[Symbol.iterator]() {
    for (let bit = 0; bit < this._bitSize; bit++) {
      yield this.isSet(bit);
    }
  }

  toUrlSafeBase64() {
    var compressedBytes = deflateRaw(this._arr, { strategy: Z_RLE, to: "string" });
    const base64 = btoa(compressedBytes);
    const makeUrlSafe = (m) => ({ "+": "-", "/": "_", "=": "" }[m]);
    return base64.replace(/[+/=]/g, makeUrlSafe);
  }

  static fromUrlSafeBase64(urlSafeBase64) {
    const makeOriginal = (match) => ({ "-": "+", _: "/" }[match]);
    const base64 = urlSafeBase64.replace(/[-_]/g, makeOriginal);
    const compressedBytes = atob(base64);
    // FIXME: handle errors
    const bytesArr = inflateRaw(compressedBytes, { strategy: Z_RLE });
    const obj = new this(bytesArr.length * 8);
    obj._arr = bytesArr;
    return obj;
  }

  set(bitPos) {
    const bytePos = Math.ceil(bitPos / 8);
    const bytePosVal = 2 ** (bitPos % 8);
    this._arr[bytePos] |= bytePosVal;
  }

  isSet(bitPos) {
    const bytePos = Math.ceil(bitPos / 8);
    const bytePosVal = 2 ** (bitPos % 8);
    return (this._arr[bytePos] & bytePosVal) !== 0;
  }
}

export default BitArray;