c - iOS 中的按位或

Question

enum {
   UIViewAnimationOptionLayoutSubviews            = 1 <<  0,
   UIViewAnimationOptionAllowUserInteraction      = 1 <<  1,
   UIViewAnimationOptionBeginFromCurrentState     = 1 <<  2,
   UIViewAnimationOptionRepeat                    = 1 <<  3,
   UIViewAnimationOptionAutoreverse               = 1 <<  4,
   UIViewAnimationOptionOverrideInheritedDuration = 1 <<  5,
   UIViewAnimationOptionOverrideInheritedCurve    = 1 <<  6,
   UIViewAnimationOptionAllowAnimatedContent      = 1 <<  7,
   UIViewAnimationOptionShowHideTransitionViews   = 1 <<  8,

   UIViewAnimationOptionCurveEaseInOut            = 0 << 16,
   UIViewAnimationOptionCurveEaseIn               = 1 << 16,
   UIViewAnimationOptionCurveEaseOut              = 2 << 16,
   UIViewAnimationOptionCurveLinear               = 3 << 16,

   UIViewAnimationOptionTransitionNone            = 0 << 20,
   UIViewAnimationOptionTransitionFlipFromLeft    = 1 << 20,
   UIViewAnimationOptionTransitionFlipFromRight   = 2 << 20,
   UIViewAnimationOptionTransitionCurlUp          = 3 << 20,
   UIViewAnimationOptionTransitionCurlDown        = 4 << 20,
};
typedef NSUInteger UIViewAnimationOptions;

这个表达式的确切含义:UIViewAnimationOptionRepeat | UIViewAnimationOptionAutoreverse.

UIViewAnimationOptionRepeat 的值等于 8(在 bin 1000 中)，UIViewAnimationOptionAutoreverse 等于 16(在 bin 10000 中)。所以表达式 UIViewAnimationOptionRepeat | UIViewAnimationOptionAutoreverse 应该按照我的想法生成 16(bin 10000) -> UIViewAnimationOptionReverse。

Answer 1

操作|由真值表定义

   | 0 | 1  
---+---+---
 0 | 0 | 1
 1 | 1 | 1

即 x | y == 0 仅当 x == 0 和 y == 0 时。 | 运算符同时作用于机器字的所有位。所以

  001000   (8)
| 010000  (16)
  ------------
  011000  (24)