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

In contrast to what others have said, the bit-twiddling trick actually can be used on any number of bits portably. Just change it a bit:

unsigned int shift = 1;

for (v--; shift < 8 * sizeof v; shift <<= 1)
{
    v |= v >> shift;
}

return ++v;

I believe any compiler will optimize the loop away, so it should be the same performence-wise (plus I think it looks better).