Question

When doing some bit twiddling and removing branches the following problem pops up from time to time:

Say I have an integer binary flag f, which can be 0 or 1. How can I turn this into respectively -1 and 1 (or the opposite way around, at your discretion – often either one is usable). A common way is this:

int i = 2*f - 1;

But this uses an addition and a multiplication. Can it be done any faster?

Answer 1

Well, for starters you can do

int i = (f << 1) - 1;

Also, you could try

int i = f - (!f);