"It is not so complicated... once you've done one."
And just to prove Guillaume's point, here is one that I built, exactly doing what Mathieu wanted at the start this thread (as he said he already wrote one).
It took me about 10 minutes, (the SDK wizards generate the base code so nicely). Of course, it goes without saying, you need some c++ knowledge, a little ICE API, and have the right compilers.
This nodes takes in a float array per point, adds array values cumulatively and output the new array. Sincerest apologies if you do not like the color of the node ; also 'fibonacci' is not a proper name for this one, as it is for natural numbers but the logic is remarkably same, so I borrowed that name.
Compiled for 64 bit, it only takes in floats and per point context but can be extended for polymorphism. If anybody is looking for some source code for writing polymorphic ICE node dealing with arrays, a good example can be found here.