<p>The first (strongly) polynomial-time algorithm was <a href="https://arxiv.org/abs/1307.6809" rel="nofollow noreferrer">published</a> by Végh in 2013, and has since been <a href="https://arxiv.org/abs/1611.01778" rel="nofollow noreferrer">improved</a> by Olver and Végh to a worst-case runtime in O((<em>m</em> + <em>n</em> log <em>n</em>) <em>m</em> <em>n</em> log(<em>n</em>^2 / <em>m</em>)). 
But I don't know of any public implementation for this algorithm.</p>

<p>The linked papers also contain references to earlier (weakly) polynomial-time algorithms as well as approximate algorithms, some of which may have public implementations. (<a href="https://www.cs.princeton.edu/~wayne/papers/gain-scaling.pdf" rel="nofollow noreferrer">This older paper</a> by Tardos and Wayne mentions a C++ implementation.)</p>
Calculating max flow in a generalized network
<p>I'm trying to find an efficient, publically available algorithm, preferably with implementation, for solving maximum flow in a generalized (non-pure) network with gains. 
All multipliers, capacities and flow values are non-zero integers. </p>

<p>Does such an algorithm exist, or is this problem not solvable in polynomial time?</p>