function crypto_stream_xor (c: Uint8Array, cpos: number, m: Uint8Array | null, mpos: number, d: number, n: Uint8Array, k: Uint8Array): number {
  const s = new Uint8Array(32);
  core(s, n, k, sigma, true);
  return crypto_stream_salsa20_xor(c, cpos, m, mpos, d, n.subarray(16), s);
}