Invert operation for bitwise in C

Question

Dear all C programmer:

X = 1 << N; (left shift)

how to recover N from X ?

Thanks

Answer 1

In a while loop, keep shifting right until X==1, record how many times you have to shift right and the counter will give you N.

int var = X;
int count = 0;
while (var != 1){
    var >>= 1; 
    count++;
}
printf("N is %d", count);