这编译为更快的code：＆QUOT; N * 3英寸或QUOT; N +（N * 2）QUOT ;? [英] Which compiles to faster code: "n * 3" or "n+(n*2)"?

问题描述

这编译更快code：ANS = N * 3或ANS = N +（N * 2）

Which compiles to faster code: "ans = n * 3" or "ans = n+(n*2)"?

假设n是不是一个int或长，并且它是在一个现代化的Win32英特尔机器上运行。

Assuming that n is either an int or a long, and it is is running on a modern Win32 Intel box.

这会是不同的，如果有一些涉及取消引用，那就是，这其中会更快？

Would this be different if there was some dereferencing involved, that is, which of these would be faster?

long    a;
long    *pn;
long     ans;

...
*pn = some_number;
ans = *pn * 3;

或者

ans = *pn+(*pn*2);

或者是一些人们不必担心因为优化编译器可能会在任何情况下，考虑到这一点？

Or, is it something one need not worry about as optimizing compilers are likely to account for this in any case?

推荐答案

IMO这种微型的优化，除非你有一些外来的编译器的工作是没有必要的。我把可读性放在首位。

IMO such micro-optimization is not necessary unless you work with some exotic compiler. I would put readability on the first place.

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