問(wèn)題描述

我使用 64 位整數(shù)中的位存儲(chǔ)標(biāo)志.
我想知道在 64 位整數(shù)中的位置是否設(shè)置了一個(gè)位(即我不關(guān)心任何特定位的位置).

I store flags using bits within a 64-bits integer.
I want to know if there is a single bit set whatever the position within the 64-bits integer (e.i. I do not care about the position of any specific bit).

boolean isOneSingleBitSet (long integer64)
{
   return ....;
}

我可以使用 Bit Twiddling Hacks 計(jì)算位數(shù)(肖恩·埃隆·安德森(Sean Eron Anderson))，但我想知道僅檢測(cè)是否設(shè)置了一個(gè)位的最有效方法是什么...

I could count number of bits using the Bit Twiddling Hacks (by Sean Eron Anderson), but I am wondering what is the most efficient way to just detect whether one single bit is set...

我發(fā)現(xiàn)了一些其他相關(guān)的問(wèn)題:

I found some other related questions:

• (8051) 檢查是否設(shè)置了單個(gè)位
• 檢測(cè)整數(shù)內(nèi)的單個(gè)一位流

還有一些維基百科頁(yè)面:

and also some Wikipedia pages:

• 查找第一個(gè)
• 位操作
• 漢明權(quán)重

注意:我的應(yīng)用程序是用 java 編寫的，但我對(duì)使用其他語(yǔ)言的優(yōu)化感到好奇...

NB: my application is in java, but I am curious about optimizations using other languages...

編輯:L?u V?nh Phúc 指出我的問(wèn)題中的第一個(gè)鏈接已經(jīng)得到了答案:請(qǐng)參閱確定整數(shù)是否為 2 的冪部分em>Bit Twiddling Hacks(作者 Sean Eron Anderson).我沒(méi)有意識(shí)到一位與二的冪是一樣的.

EDIT: L?u V?nh Phúc pointed out that my first link within my question already got the answer: see section Determining if an integer is a power of 2 in the Bit Twiddling Hacks (by Sean Eron Anderson). I did not realized that one single bit was the same as power of two.

推薦答案

如果您只是想檢查是否設(shè)置了一個(gè)位，那么您實(shí)際上是在檢查該數(shù)字是否是 2 的冪.要做到這一點(diǎn)，您可以做:

If you just literally want to check if one single bit is set, then you are essentially checking if the number is a power of 2. To do this you can do:

if ((number & (number-1)) == 0) ...

這也將 0 視為 2 的冪，因此如果這很重要，您應(yīng)該檢查不是 0 的數(shù)字.那么:

This will also count 0 as a power of 2, so you should check for the number not being 0 if that is important. So then:

if (number != 0 && (number & (number-1)) == 0) ...

這篇關(guān)于檢查整數(shù)中是否只設(shè)置了一個(gè)位(無(wú)論其位置如何)的文章就介紹到這了，希望我們推薦的答案對(duì)大家有所幫助，也希望大家多多支持html5模板網(wǎng)！