Fast 1/X division (reciprocal)

Question

Is there some way to improve reciprocal (division 1 over X) with respect to speed, if the precision is not crucial?

So, I need to calculate 1/X. Is there so

Answer 1

First of all, if you turn on compiler optimizations, the compiler is likely to optimize the calculation if possible (to pull it out of a loop, for example). To see this optimization, you need to build and run in Release mode.

Division may be heavier than multiplication (but a commenter pointed out that reciprocals are just as fast as multiplication on modern CPUs, in which case, this isn't correct for your case), so if you do have 1/X appearing somewhere inside a loop (and more than once), you can assist by caching the result inside the loop (float Y = 1.0f/X;) and then using Y. (The compiler optimization might do this in any case.)

Also, certain formulas can be redesigned to remove division or other inefficient computations. For that, you could post the larger computation being performed. Even there, the program or algorithm itself can sometimes be restructured to prevent the need for hitting time-consuming loops from being hit as frequently.

How much accuracy can be sacrificed? If on the off chance you only need an order of magnitude, you can get that easily using the modulus operator or bitwise operations.

However, in general, there's no way to speed up division. If there were, compilers would already be doing it.