2的N次幂相关计算

计算  2Λ(n-1) < v <2Λ(n-1)

uint32_t RoundUpPow2(uint32_t v)
 {
    v--;
    v |= v >> 1;    v |= v >> 2;
    v |= v >> 4;    v |= v >> 8;
    v |= v >> 16;
    return v+1;
}

判断是否是2的n次幂

bool IsPowerOf2(int v)
 {
    return (v & (v - 1)) == 0;
}