Concentus interpreted almost all C pointers as a combination of an array and an integer offset, e.g. "int[] x, int x_ptr". These could potentially all be replaced by new Span constructs in .NetCore 2.0 for better optimization. Furthermore, most stack array allocations are done on the heap in C#, which also yields bad performance (except where they were hand-inlined inside the FFT)
See https://msdn.microsoft.com/en-us/magazine/mt814808.aspx