[Algorithms] Fast SH squaring

[Ben Y. <shu...@gm...>]

Hi guys,

I've been catching up on some of the global illumination literature
recently, and I found the SH exponentiation paper by Ren et al especially
interesting.

There's one paragraph however where it's mentioned that "SH squares are also
cheaper than general SH products" (ie, computing F * F is more efficient
than F * G), but which is not elaborated on. Sadly, the details are not
immediately obvious to me. Can someone shed some light on how and why?
Apparently, this is efficient enough to compute in the GPU (unlike a general
SH triple product).

Thanks,
Ben Yeoh