This is an interview question:  

You are given a char variable named `ch`, when you know that it represents a number that in its binary form, only one of its eight bits will be equal to '1'. I.E. , the only possible values for `ch` are: `0x1, 0x2, 0x4, 0x8, 0x10, 0x20, 0x40, 0x80`.  

Given the variable `ch`, I need to write the most efficient code to get the index of that '1' bit. For example: if `ch == 0x1` -> result is 0. if `ch == 0x4` -> result is 2. 

The obvious way is to use switch-case, but I need something more efficient.  

Is there any bit manipulation you can do here for efficient implementation?