[defrost]

> For a while I was thinking I should recompute the SG coefficients every time

We had, in our geophysics application, a "pre computed" coefficient cache - the primary filters (central symmetric smoothing at various lengths) were common choices and almost always there to grab - missing values were either cheaply "faked" for Quick'NDirty displays or infilled by prediction filters that were S-G's computed to use existing points within the range to replace the missing value, that was either a look up from indexed filter cache or a fresh filter generation to use and stash in cache.

It's a complication (in the mechanical watch sense) to add, but with code to generate coefficients already existing it's really just looking at the generation times versus the hassle of indexing and storing them as created and the frequency of reuse of "uncommon" patterns.