# `Mojoler.Twice`
[🔗](https://github.com/thanos/mojoler/blob/v0.1.0/lib/mojoler/twice.ex#L1)

Checked doubling of a signed 64-bit integer, loaded from `priv/native/libtwice.so`.

The native file imports the generated ABI. It does not declare `ErlNifFunc`
or `ErlNifEntry`.

# `i64`

```elixir
@type i64() :: -9_223_372_036_854_775_808..9_223_372_036_854_775_807
```

A signed 64-bit integer.

# `double`

```elixir
@spec double(i64()) :: i64()
```

Returns `2 * n` when `n` and the product fit in a signed 64-bit integer.

`n` is an integer. There is no optional argument.

## Returns

The product, an integer.

## Raises

  * `ArgumentError` when `n` is not an integer, does not fit in signed 64 bits,
    or `2 * n` would overflow

## Examples

    iex> Mojoler.Twice.double(21)
    42

    iex> Mojoler.Twice.double(0)
    0

    iex> Mojoler.Twice.double(-3)
    -6

    iex> Mojoler.Twice.double(:nope)
    ** (ArgumentError) argument error

    iex> Mojoler.Twice.double(9_223_372_036_854_775_807)
    ** (ArgumentError) argument error

# `load_nif`

```elixir
@spec load_nif() :: :ok | {:error, term()}
```

Loads `priv/native/libtwice.so`.

A second call in the same VM returns `{:error, {:reload, charlist}}`.

## Examples

    iex> Mojoler.Twice.load_nif()
    {:error, {:reload, ~c"NIF library already loaded (reload disallowed since OTP 20)."}}

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*Consult [api-reference.md](api-reference.md) for complete listing*