C快速计算下一个4的倍数? [英] C quick calculation of next multiple of 4?

问题描述

将无符号int舍入为4倍数的快速方法是什么?

What's a fast way to round up an unsigned int to a multiple of 4?

4的倍数具有两个最低有效位0，对吗?所以我可以将它们屏蔽掉，然后执行switch语句，将1,2或3添加到给定的uint.

A multiple of 4 has the two least significant bits 0, right? So I could mask them out and then do a switch statement, adding either 1,2 or 3 to the given uint.

这不是一个非常优雅的解决方案.

That's not a very elegant solution..

还有算术综述:

 myint == 0 ? 0 : ((myint+3)/4)*4

也许有更好的方法进行一些位操作?

Probably there's a better way including some bit operations?

推荐答案

(myint + 3) & ~0x03

3的加法使得4的下一个倍数成为4的上一个倍数，这是通过模运算产生的，因为除数是2的幂，所以可以通过掩膜实现.

The addition of 3 is so that the next multiple of 4 becomes previous multiple of 4, which is produced by a modulo operation, doable by masking since the divisor is a power of 2.

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