So I did some researching into LED gamma correction and then realized that using v (which is 0…1, not 0-255) meant the table approach was awkward (but doable), but decided to compare the v*v (and v * v * v) approach to the results from the gamma 2.8 version of the 0-255 table (converted to 0…1 format for v), and behold:
v * v * v is so close as to make no difference, while v*v isn’t quite as good but is probably ‘good enough’ for most purposes.
While it might be nice if @wizard added a gamma function (especially for higher bits/HDR) for speed purposes, so long as you are ok with cubing v, you might as well do that.