Question

I have an int parameter with the possible values 1,2,4,8,16,32,64.

I need to know the bit offset of the current value, i.e. for each value return 1, 2, 3, 4, 5, or 6 respectively.

What is the easiest way to achieve that?

Answer 1

You have multiple answers here : http://graphics.stanford.edu/~seander/bithacks.html#IntegerLogObvious
the easiest being, assuming you have your input value in an unsigned int v :

unsigned int r = 0; // r will be lg(v)

while (v >>= 1) // unroll for more speed...
{
  r++;
}

but it will change v in the process.

edit: in your case if you are 100% sure your input is and int and a power of 2, a look-up-table may be the simplest and fastest