如何创建与面膜至少significat位用设定为1 [英] How to create mask with least significat bits set to 1 in C

问题描述

有人能请解释一下这个功能对我？

Can someone please explain this function to me?

一个面具设置为1的最低显著n位。

A mask with the least significant n bits set to 1.

例如：

N = 6 - >值为0x2F，N = 17 - > 0x1FFFF //我不明白这些可言，尤其是如何每组6 - >值为0x2F

n = 6 --> 0x2F, n = 17 --> 0x1FFFF // I don't get these at all, especially how n = 6 --> 0x2F

此外，什么是面具？

推荐答案

通常的方法是采取 1 和移位它留下ñ 位。这会给你是这样的： 00100000 。然后减去一个来自这一点，这将清除的设置位，并设置所有的少显著位，所以在这种情况下，我们会得到： 00011111

The usual way is to take a 1, and shift it left n bits. That will give you something like: 00100000. Then subtract one from that, which will clear the bit that's set, and set all the less significant bits, so in this case we'd get: 00011111.

一个面具通常用位操作使用，特别是和。你会使用上面的面具由​​自己来获得至少5位显著，二话不说，可能是present隔离。与将通常具有包含比特重新presenting若干完全独立的，不相关的数量和/或标志的单个硬件寄存器硬件处理时，这是特别普遍的。

A mask is normally used with bitwise operations, especially and. You'd use the mask above to get the 5 least significant bits by themselves, isolated from anything else that might be present. This is especially common when dealing with hardware that will often have a single hardware register containing bits representing a number of entirely separate, unrelated quantities and/or flags.

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