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Last active April 11, 2018 08:44
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一些位运算的技巧
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bit.md

n个bit能表示的最大数值

-1 ^ (-1<<n) = 2^n-1

原理：将最右n位变成1

  • -1 表示 1111 1111 1111 1111
  • 移4位后 1111 1111 1111 1111 0000
  • 高位舍去，异或
     1111 1111 1111 0000
^    1111 1111 1111 1111             
---------------------------            
     0000 0000 0000 1111

PS: a & mask = a % mask

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