Anyone have an opinion on what existing block is closest to the attached so that I can start writing

Attached is a C implementation of a block I wish was in Gnu Radio.
Anyone done anything similar-enough as a block
in Gnu Radio that would make a decent starting point?

It’s basically a block that takes a fixed-size vector input, and a list
of “descriptors” that describe output channels that need to be carved
out of
the input vector (a list of start:end which are simply offsets into
the vector). It’s intended to be used after a FFT+complex-to-MAG block
process the resulting vector and select sub-bands and turn them into
power-estimate channels. I see nothing in Gnu Radio that does this,
other than things like the FFT channelizer, PFB channelizer, etc.
Neither of those is efficient in this case, because the channels are of
non-uniform distribution and width, and if the target is simply power
estimation, that part has already basically been done by the
FFT+complex-to-MAG stage.