FastLED is about more than just pushing data out to leds as quickly as possible. It is also about providing the fastest supporting function (math, color maniuplation, etc...) while still remaining accurate. Mark has done an amazing job with many of the math functions, including fast trig functions that are ~98% accurate, and the core of the scaling functions. These scaling functions are what allow us to do things like the non-destructive, 0 overhead scaling and color adjustments in the library.
The basic scaling function in FastLED is scale8. It lets you scale an 8-bit value by another 8-bit value. It's a percentage of sorts, but from 0-255 instead of 0-100. So, for example, scale8(64,128) will give you 32. Scaling is something that gets used a lot in led work, so it is important that it be fast. The C version of scale8 takes advantage of some properties of binary math to do it's magic (while avoiding division), let's take a look:
uint8_t scale8(uint8_t i, fract8 s