Add *Math.nextPowerOfTwo

There are existing *Math.isPowerOfTwo methods, it seems like a nextPowerOfTwo method is a good method to go alongside it, to return the smallest integer >= n that is a power of two (I was surprised this doesn’t exist in guava already, TBH)

This is a simple operation that has a wide range of applications (sizing buffers, primarily, but it also has uses in collection implementations etc), and it’s not immediately obvious what the bit-twiddling algorithm is doing when it appears in a codebase. Would seem like a prime candidate for an addition to guava.

There’s a simple bit-twiddling algorithm for ints & longs; doubles & bigintegers can probably use a combination of the existing log, floor & pow methods, unless there are clever ways of doing the same for those types (also see http://stackoverflow.com/questions/466204/rounding-up-to-nearest-power-of-2)

[leventov]

@ben-manes thank you. Google (the search engine, not the company) is somehow bad at finding methods in published Guava’s Javadocs.

[ben-manes]

A simple version of that is below, which is what I use. As its a one-liner I put the method in the class since its only rarely needed.

static int ceilingNextPowerOfTwo(int x) {
  // From Hacker's Delight, Chapter 3, Harry S. Warren Jr.
  return 1 << (Integer.SIZE - Integer.numberOfLeadingZeros(x - 1));
}