How to write a better strlen function?

c string optimization pointers c-strings
Victor picture Victor · Jul 5, 2011 · Viewed 10.6k times · Source

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;
}

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?

Answer

Mojo Risin picture Mojo Risin · Jul 5, 2011

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

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.

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

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

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