Question

given the following statement which is executed a lot:

iNormVal = iVal / uRatio;

would the following make more sense (performance wise) if uRatio == 1 most (90%) of the time?

if(uRatio > 1)
iNormVal = iVal / uRatio;
else
iNormVal = iVal;

thanks..

Answer 1

You need to profile this to get a measurement, it’s too hard to guess. The compiler might decide you’re wrong and remove the test, so check with and without optimizing.

The actual cost of an (integer) division might be rather low, especially on modern desktop-class processors. According to this PDF, the costs on modern (Wolfdale/Nehalem/Sandy Bridge) of a 32/32-bit division are 14-23/17-28/20-28 cycles respectively. So, if you really do this a lot, it might add up. In that case, look into parallel (vectorized) options if possible.

I would try to avoid it if at all possible, since it introduces a branch. Branches have two disadvantages: they make the code more complex by introducing multiple paths that the programmer reading the code has to understand, and they can also introduce execution overhead.