### Number of 1s in 2's complement representation

**Source:**Interview Street CodeSprint (slightly modified)

**Problem:**

One of the basics of Computer Science is knowing how numbers are represented in 2's complement. Imagine that you write down all numbers between A and B inclusive in 2's complement representation using 32 bits. How many 1's will you write down in all ?

**Input:**

Two integers A and B

**Output:**

The number of 1s

**Constraints:**

-2^31 <= A <= B <= 2^31 - 1

Find the asymptotically optimal algorithm.