Write a C function that round up a number to next power of 2

Question

I got the following question in an interview: \"Write a C function that round up a number to next power of 2.\"

I wrote the following answer:

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Answer 1

Such questions always deserve counter questions to clarify requirements, if only to demonstrate your thinking and analytical skills and even creativity - that is what the interview should be about.

For example in the absence of any specification that the "number" in question is necessarily an integer, you might propose the following:

int nextPow2( double x )
{
    return (int)pow( 2, ceil(log10(x) / log10(2))) ;
}

But if you did you might also express concern about the applicability of such a solution to an embedded system with possibly no floating-point unit.