```
bit_count(i)
```

Return the number of bits set in the integer `i`

.

For nonnegative inputs, `bit_count`

will return the number of bits set in the two's complement
representation of `i`

. For negative inputs, it returns a negative number whose magnitude
is one greater than the number of bits not set in the two's complement representation of `i`

.

```
bit_count(5)
// 2
```