docs: function crypto_stream_salsa20_xor(c,cpos,m,mpos,b,n,k) {
    var z = new Uint8Array(16), x = new Uint8Array(64);
    var u, i;
    for (i = 0; i < 16; i++) z[i] = 0;
    for (i = 0; i < 8; i++) z[i] = n[i];
    while (b >= 64) {
      crypto_core_salsa20(x,z,k,sigma);
      for (i = 0; i < 64; i++) c[cpos+i] = m[mpos+i] ^ x[i];
      u = 1;
      for (i = 8; i < 16; i++) {
        u = u + (z[i] & 0xff) | 0;
        z[i] = u & 0xff;
        u >>>= 8;
      }
      b -= 64;
      cpos += 64;
      mpos += 64;
    }
    if (b > 0) {
      crypto_core_salsa20(x,z,k,sigma);
      for (i = 0; i < b; i++) c[cpos+i] = m[mpos+i] ^ x[i];
    }
    return 0;
  }