function crypto_stream_salsa20_xor (c: Uint8Array, cpos: number, m: Uint8Array | null, mpos: number, b: number, n: Uint8Array, k: Uint8Array): number {
  const z = new Uint8Array(16), x = new Uint8Array(64);
  let u, i;
  if (!b) return 0;
  for (i = 0; i < 16; i++) z[i] = 0;