How to calculate big O notation according to number width?

I'm trying to understand big O with the bitwise operations. I have 2 functions those are solving the same question from different perspective.

num1BitsSecondSolution starts to shift the number right until number is 0. So Complexity looks like = O(width(n)) but how could I notate width ?

num1BitsThirdSolution it is more complex to calculate it's respected complexity because it just do number = number & (number - 1) which is based on number's initial bit representation form. Example : If there are 4 "1" bits in the number then complexity is O(4) so how could I explain these in Big O ?

function num1BitsSecondSolution($number)
{
    if ($number <= 0) {
        return 0;
    }

    for ($c = 0; $number; $number >>= 1) {
        $c += $number & 1;
    }

    return $c;
}

function num1BitsThirdSolution($number)
{
    if ($number <= 0) {
        return 0;
    }

    for ($c = 0; $number; $c++) {
        $number &= $number - 1;
    }

    return $c;
}