位运算符比一般的算术运算符速度要快，而且可以实现一些算术运算符不能实现的功能。如果要开发高效率程序，位运算符是必不可少的。位运算符用来对二进制位进行操作，包括：按位与（&）、按位或（|）、按位异或（^）、按位取反（~）、按位左移（<<）、按位右移（>>）。下面就给大家介绍位运算符的详细用法。
一、按位与 and（&）
对两个数进行操作，然后返回一个新的数，这个数的每个位都需要两个输入数的同一位都为1时才为1，如下：
相同位的两个数字都为1，则为1；若有一个不为1，则为0。
00101
11100
----------------
00100
二、按位或 or（|）
比较两个数，然后返回一个新的数，这个数的每一位设置1的条件是两个输入数的同一位都不为0(即任意一个为1，或都为1)，如下：
相同位只要一个为1即为1。
00101
11100
----------------
11101
三、按位异或 xor（^）
比较两个数，然后返回一个数，这个数的每个位设为1的条件是两个输入数的同一位不同，如果相同就设为0，
xor运算的逆运算是它本身，也就是说两次异或同一个数最后结果不变，即（a xor b) xor b = a。xor运算可以用于简单的加密，比如我想对我MM说1314520，但怕别人知道，于是双方约定拿我的生日19880516作为密钥。1314520 xor 19880516 = 20665500，我就把20665500告诉MM。MM再次计算20665500 xor 19880516的值，得到1314520。
如下：
00101
11100
----------------
11001
四、按位取反 not（~）
对一个操作数的每一位都取反，如下：
00101
----------------
11010
五、按位左移 shl（<<）
将操作数的所有位向左移动指定的位数，右末位补0。如下左移一位：
00101
----------------
01010
六、按位右移 shr（<<）
将操作数的所有位向又移动指定的位数，左末位补0.如下右移一位：
00101
----------------
00010
七、优先级
C语言中位运算符之间，按优先级顺序排列为
1 ~
2 <<、>>
3 &
4 ^
5 |
6 &=、^=、|=、<<=、>>=
八、iOS中的应用，在iOS中NS_OPTION就是用利用位运算来实现的。举例说明：
typedefNS_OPTIONS(NSUInteger, SDWebImageOptions) {
/**
* By default, when a URL fail to be downloaded, the URL is blacklisted so the library won't keep trying.
* This flag disable this blacklisting.
*/
SDWebImageRetryFailed =1<<0,
/**
* By default, image downloads are started during UI interactions, this flags disable this feature,
* leading to delayed download on UIScrollView deceleration for instance.
*/
SDWebImageLowPriority =1<<1,
/**
* This flag disables on-disk caching
*/
SDWebImageCacheMemoryOnly =1<<2,
/**
* This flag enables progressive download, the image is displayed progressively during download as a browser would do.
* By default, the image is only displayed once completely downloaded.
*/
SDWebImageProgressiveDownload =1<<3,
/**
* Even if the image is cached, respect the HTTP response cache control, and refresh the image from remote location if needed.
* The disk caching will be handled by NSURLCache instead of SDWebImage leading to slight performance degradation.
* This option helps deal with images changing behind the same request URL, e.g. Facebook graph api profile pics.
* If a cached image is refreshed, the completion block is called once with the cached image and again with the final image.
*
* Use this flag only if you can't make your URLs static with embedded cache busting parameter.
*/
SDWebImageRefreshCached =1<<4,
/**
* In iOS 4+, continue the download of the image if the app goes to background. This is achieved by asking the system for
* extra time in background to let the request finish. If the background task expires the operation will be cancelled.
*/
SDWebImageContinueInBackground =1<<5,
/**
* Handles cookies stored in NSHTTPCookieStore by setting
* NSMutableURLRequest.HTTPShouldHandleCookies = YES;
*/
SDWebImageHandleCookies =1<<6,
/**
* Enable to allow untrusted SSL certificates.
* Useful for testing purposes. Use with caution in production.
*/
SDWebImageAllowInvalidSSLCertificates =1<<7,
/**
* By default, images are loaded in the order in which they were queued. This flag moves them to
* the front of the queue.
*/
SDWebImageHighPriority =1<<8,
/**
* By default, placeholder images are loaded while the image is loading. This flag will delay the loading
* of the placeholder image until after the image has finished loading.
*/
SDWebImageDelayPlaceholder =1<<9,
/**
* We usually don't call transformDownloadedImage delegate method on animated images,
* as most transformation code would mangle it.
* Use this flag to transform them anyway.
*/
SDWebImageTransformAnimatedImage =1<<10,
/**
* By default, image is added to the imageView after download. But in some cases, we want to
* have the hand before setting the image (apply a filter or add it with cross-fade animation for instance)
* Use this flag if you want to manually set the image in the completion when success
*/
SDWebImageAvoidAutoSetImage =1<<11
};
传值的时候可以用按位或（|）来传多个值，如，options = SDWebImageRetryFailed|SDWebImageLowPriority|SDWebImageCacheMemoryOnly，判断的时候再进行一次按位与（&）运算，判断是否为真，如,options&SDWebImageRetryFailed，判断上述 值为真就可以了