Hue Shift

Ok. The HSV formula for transferring RGB triplet into the HSV form is widely published. But I've failed to find any hints to how one arrives at it, so I could try to optimize it for my game's blitter routine. Therefore I tried to infer h,s,v formula myself, using basic vector math.

v = (r+g+b)/3 //value
hs = v-r,v-g,v-b //hue*saturation vector
s = hs.length //saturation
h = angle(hs/s) //hue is the angle of the vector

Guess when one needs to just change the saturation, there is no reason compute the angle or even vector length in full, but the common requirement to change the hue requires nasty computation. Can anyone hint at any efficient way of shifting hue?

>>36
everything depends on how much accuracy you want to sacrifice for speed, how fast you really need to be and do you have other requirements like memory use. iterative methods based on Newton's formula are a classic, and you can set max number of iterations to control the tradeoff. if this isn't enough, pre-computed lookup tables can help. here's a solution using those made by some stackoverflowgrammer: https://stackoverflow.com/a/1100591