function nextPow2(v) {
    v += v === 0 ? 1 : 0;
    --v;
    v |= v >>> 1;
    v |= v >>> 2;
    v |= v >>> 4;
    v |= v >>> 8;
    v |= v >>> 16;
    return v + 1;
}
Rounds to next power of two.
@function nextPow2
@memberof PIXI.utils
@param {number} v - input value
@returns {number} - next rounded power of two