Given a **32 bit** 2's complement number and the bitwise operation set **&** (and), **|** (or), **^** (xor), **<<** and **>** (left and right shifting) define an equation or algorithm to count the number of bits which are set to 1 in the string without looping structures. Registers (variables) are allowed.

In other words: write the following C function without loops:

int set_bits_count(int input) {

}