rgb to yuv420 algorithm efficiency

Question

I wrote an algorithm to convert a RGB image to a YUV420. I spend a long time trying to make it faster but I haven\'t find any other way to boost its efficiency, so now I turn to

Answer 1

The only obvious point I can see is that you're doing 3 * i three times. You could store that result in a local variable but the compiler may well already be doing that. So..

r = rgb + 3 * i;
g = rgb + 3 * i + 1;
b = rgb + 3 * i + 2;

...becomes:

r = rgb + 3 * i;
g = r + 1;
b = g + 1;

..although I doubt it'd have much impact.

As ciphor suggests, I think assembly is the only way you're likely to improve upon what you've got there.