C＃中的数学问题：2最小功率大于x？ [英] C# math question: smallest power of 2 bigger than X?

问题描述

    public int CalcBrackets(int teamCount)
    {
        int positions = 1;

        while (positions < teamCount)
            positions *= 2;

        return positions;
    }

我想是2和大于或等于电源的最小数teamCount。这真的是做到这一点的最好方法是什么？它看起来很可怕：（

I want the smallest number that is a power of 2 and bigger or equal than teamCount. Is this really the best way to do it? It sure looks horrible :(

推荐答案

如果你需要计算的2最少的功率（而不是多个）较小的话teamCount，然后可能是最好的方法。以对数是costy操作，可以把更多的时间，那么一个简单的循环。

If you need to calculate the least power of 2 (not the multiple) smaller then teamCount, then possibly it is the best way. Taking logarithm is a costy operation and can take more time then a simple cycle.

UPD
给一个算法使用位操作（C ++）（http://aggregate.org/MAGIC/，节下一个最大的2电源）

upd Here is an algorithm (C++) using bitwise operations (http://aggregate.org/MAGIC/, section Next Largest Power of 2)

unsigned int nlpo2(unsigned int x)
{
    x--; // comment out to always take the next biggest power of two, even if x is already a power of two
    x |= (x >> 1);
    x |= (x >> 2);
    x |= (x >> 4);
    x |= (x >> 8);
    x |= (x >> 16);
    return (x+1);
}

首先，它设置数与那些所有相关的位（例如，为0x3FF），然后递增它（0x400的），以获得两个电源。

First, it sets all relevant bits of the number to ones (for example, 0x3ff) and then increments it (0x400) to get the power of two.

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