如何写出更好的strlen函数？ [英] How to write a better strlen function?

问题描述

我读写大code卷2，并显示以下的strlen impelementation：

I am reading "Write Great Code Volume 2" and it shows the following strlen impelementation:

int myStrlen( char *s )
{
    char *start;
    start = s;
    while( *s != 0 )
    {
        ++s;
    }
    return s - start;
}

书上说，这实现是典型的缺乏经验的C程序员。我已经用C编码在过去的11年，我不知道怎样写一个函数比这更好的在C（我能想到用汇编编写更好的东西）。这怎么可能写出code比在C更好？我看了标准库实现glibc中的strlen函数和我无法理解它的大部分。我在哪里可以找到关于如何编写高度优化的code更好的信息？

the book says that this implementation is typical for an inexperienced C programmer. I have been coding in C for the past 11 years and i can't see how to write a function better than this in C(i can think of writing better thing in assembly). How is it possible to write code better than this in C? I looked the standard library implementation of the strlen function in glibc and I couldn't understand most part of it. Where can I find better information on how to write highly optimized code?

推荐答案

的strlen （），一个由博文科尔姆·MacCarthaigh：

From Optimising strlen(), a blogpost by Colm MacCarthaigh:

不幸的是C，我们注定要为O（n）的实现，最好的情况下，但我们仍然没有这样做......我们能做点什么n的极具规模。

Unfortunately in C, we’re doomed to an O(n) implementation, best case, but we’re still not done … we can do something about the very size of n.

这使在什么方向就可以工作，加快它很好的例子。而且从它的另一个报价

It gives good example in what direction you can work to speed it up. And another quote from it

有时候会真的快只是让你真的疯了。

Sometimes going really really fast just makes you really really insane.

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