IP.prev

You're seeing just the function prev, go back to IP module for more information.

Specs

prev(v4()) :: v4()
prev(v6()) :: v6()

returns the previous ip address.

iex> IP.prev({10, 0, 1, 0})
{10, 0, 0, 255}

iex> IP.prev({0, 0, 0, 0, 0, 0, 1, 0})
{0, 0, 0, 0, 0, 0, 0, 0xFFFF}