C/C#中的模数更快?

问题描述

对于特定的基数，是否可以创建比标准％运算符更快的整数模数?

对于我的程序，我需要大约1000-4000(例如n％2048).有没有比简单地执行n模数2048更快的方法?n%2048?

解决方案

如果在编译时知道分母为2的幂，例如2048，则可以减去1并进行按位与运算. /p>

也就是说:

n % m == n & (m - 1) 

...其中m是2的幂.

例如:

22 % 8 == 22 - 16 == 6

         Dec   Bin
       -----   -----
          22 = 10110
           8 = 01000  
       8 - 1 = 00111 
22 & (8 - 1) =   10110 
               & 00111 
               -------
           6 =   00110

请记住，一个好的编译器将对%进行自己的优化，甚至可能与上述技术一样快.算术运算符往往会进行大量优化.

Is there a trick for creating a faster integer modulus than the standard % operator for particular bases?

For my program, I'd be looking for around 1000-4000 (e.g. n%2048). Is there a quicker way to perform n modulus 2048 than simply: n%2048?

解决方案

If the denominator is known at compile time to be a power of 2, like your example of 2048, you could subtract 1 and do a bitwise-and.

That is:

n % m == n & (m - 1) 

...where m is a power of 2.

For example:

22 % 8 == 22 - 16 == 6

         Dec   Bin
       -----   -----
          22 = 10110
           8 = 01000  
       8 - 1 = 00111 
22 & (8 - 1) =   10110 
               & 00111 
               -------
           6 =   00110

Bear in mind that a good compiler will have its own optimizations for %, maybe even enough to be as fast as the above technique. Arithmetic operators tend to be pretty heavily optimized.

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