text: import {
    StreamCipher,
  } from './cipher-core.js';
  
  function generateKeystreamWord() {
    // Shortcuts
    const S = this._S;
    let i = this._i;
    let j = this._j;
  
    // Generate keystream word
    let keystreamWord = 0;
    for (let n = 0; n < 4; n += 1) {
      i = (i + 1) % 256;
      j = (j + S[i]) % 256;
  
      // Swap
      const t = S[i];
      S[i] = S[j];
      S[j] = t;
  
      keystreamWord |= S[(S[i] + S[j]) % 256] << (24 - n * 8);
    }
  
    // Update counters
    this._i = i;
    this._j = j;
  
    return keystreamWord;
  }
  
  /**
   * RC4 stream cipher algorithm.
   */
  export class RC4Algo extends StreamCipher {
    _doReset() {
      // Shortcuts
      const key = this._key;
      const keyWords = key.words;
      const keySigBytes = key.sigBytes;
  
      // Init sbox
      this._S = [];
      const S = this._S;
      for (let i = 0; i < 256; i += 1) {
        S[i] = i;
      }
  
      // Key setup
      for (let i = 0, j = 0; i < 256; i += 1) {
        const keyByteIndex = i % keySigBytes;
        const keyByte = (keyWords[keyByteIndex >>> 2] >>> (24 - (keyByteIndex % 4) * 8)) & 0xff;
  
        j = (j + S[i] + keyByte) % 256;
  
        // Swap
        const t = S[i];
        S[i] = S[j];
        S[j] = t;
      }
  
      // Counters
      this._j = 0;
      this._i = this._j;
    }
  
    _doProcessBlock(M, offset) {
      const _M = M;
  
      _M[offset] ^= generateKeystreamWord.call(this);
    }
  }
  RC4Algo.keySize = 256 / 32;
  RC4Algo.ivSize = 0;
  
  /**
   * Shortcut functions to the cipher's object interface.
   *
   * @example
   *
   *     var ciphertext = CryptoJS.RC4.encrypt(message, key, cfg);
   *     var plaintext  = CryptoJS.RC4.decrypt(ciphertext, key, cfg);
   */
  export const RC4 = StreamCipher._createHelper(RC4Algo);
  
  /**
   * Modified RC4 stream cipher algorithm.
   */
  export class RC4DropAlgo extends RC4Algo {
    constructor(...args) {
      super(...args);
  
      /**
       * Configuration options.
       *
       * @property {number} drop The number of keystream words to drop. Default 192
       */
      Object.assign(this.cfg, { drop: 192 });
    }
  
    _doReset() {
      super._doReset.call(this);
  
      // Drop
      for (let i = this.cfg.drop; i > 0; i -= 1) {
        generateKeystreamWord.call(this);
      }
    }
  }
  
  /**
   * Shortcut functions to the cipher's object interface.
   *
   * @example
   *
   *     var ciphertext = CryptoJS.RC4Drop.encrypt(message, key, cfg);
   *     var plaintext  = CryptoJS.RC4Drop.decrypt(ciphertext, key, cfg);
   */
  export const RC4Drop = StreamCipher._createHelper(RC4DropAlgo);
  