在PHP中位操作？ [英] Bitwise operations in PHP?

问题描述

据我了解，位运算所必需的很多低级编程，如编写设备驱动程序，低级别的图形，通信协议的分组组装和解码。我一直在做PHP几年来，我已经在PHP项目很少​​见到位运算。

I understand that bitwise operations are necessary for much low-level programming, such as writing device drivers, low-level graphics, communications protocol packet assembly and decoding. I have been doing PHP for several years now, and I have seen bitwise operations very rarely in PHP projects.

您能给我使用的例子？

推荐答案

您可以使用它来位掩码EN事情code组合。基本上，它的工作原理是让每个比特的含义，所以如果你有 00000000 ，每一位再presents东西，除了是一个十进制数为好。比方说，我有我想要存储用户的一些preferences，但我的数据库在存储方面非常有限。我可以简单地存储十进制数，从这个派生，其中preferences选择，例如 9 是 2 ^ 3 + 2 ^ 0 是 00001001 ，所以用户preference 1和preference 4。

You could use it for bitmasks to encode combinations of things. Basically, it works by giving each bit a meaning, so if you have 00000000, each bit represents something, in addition to being a single decimal number as well. Let's say I have some preferences for users I want to store, but my database is very limited in terms of storage. I could simply store the decimal number and derive from this, which preferences are selected, e.g. 9 is 2^3 + 2^0 is 00001001, so the user has preference 1 and preference 4.

 00000000 Meaning       Bin Dec    | Examples
 │││││││└ Preference 1  2^0   1    | Pref 1+2   is Dec   3 is 00000011
 ││││││└─ Preference 2  2^1   2    | Pref 1+8   is Dec 129 is 10000001
 │││││└── Preference 3  2^2   4    | Pref 3,4+6 is Dec  44 is 00101100
 ││││└─── Preference 4  2^3   8    | all Prefs  is Dec 255 is 11111111
 │││└──── Preference 5  2^4  16    |
 ││└───── Preference 6  2^5  32    | etc ...
 │└────── Preference 7  2^6  64    |
 └─────── Preference 8  2^7 128    |

进一步阅读

• http://www.weberdev.com/get_example-3809.html


• http://stu.mp/2004/ 06 / A-快位掩码-HOWTO换programmers.html


• 为什么要使用按位/掩码在PHP？


• http://en.wikipedia.org/wiki/Mask_%28computing%29

• http://www.weberdev.com/get_example-3809.html
• http://stu.mp/2004/06/a-quick-bitmask-howto-for-programmers.html
• Why should I use bitwise/bitmask in PHP?
• http://en.wikipedia.org/wiki/Mask_%28computing%29

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