Re: [PATCH] strlen

Arjan van de Ven (root@fenrus.demon.nl)
Thu, 28 Oct 1999 22:28:54 +0200 (CEST)

> Here is an optimized strlen function for i586+ processors, it works by
> testing 4 bytes at a time and averages 1.8 clock cycles per byte (scas =
> 4n).

This, I think, is a problem on i386. You _cannot_ read beyond the end of the
string (might be on an other, unmapped page), but you don't know that until
you do, when doing 4 bytes at a time. I mean: You can only know that you
went to far...

ia64 DOES allow this by doing the memload conditional and allowing
soft/local pagefaults to end the loop. Ask the Trilian guys about this if
you want to know more...

Greetings,
Arjan van de Ven

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