使用库函数还是按位运算?哪种方法更有效? [英] Using library functions or bitwise operations? Which method is more efficient?

问题描述

方法1

if ((size & (!(size & (size - 1)))) == size)//if size is exact power of 2
{
    alignedSegmentSize = size;
}
else
{
    while( size != 0)
    {
        size = size << 1;
        alignedSegmentSize = alignedSegmentSize + 1;
    }
    alignedSegmentSize = alignedSegmentSize << 1;
}

方法2

Method 2

double alignedSegment = log(static_cast<double>(size))/(log(TWO));
alignedSegment = (ceil((alignedSegment)));
int nextBufferSize = pow(2,alignedSegment);

我想知道对于给定值，哪种方法将更有效地计算2的最接近幂.


在此先感谢

I wanted to know which method will be more efficient to calculate the nearest power of two for the given value.


Thanks in advance

推荐答案

当然是使用按位运算的.看看检查整数是否为C的2的幂的十种方法" [

The one using bitwise operations, of course. Have a look at "Ten Ways to Check if an Integer Is a Power Of Two in C"[^]

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