RFC: MI strlen()

Sean C. Farley scf at FreeBSD.org
Thu Jan 8 20:43:57 PST 2009

On Thu, 8 Jan 2009, Xin LI wrote:

> Hi,
> Here is a new implementation of strlen() which employed the bitmask 
> skill in order to achieve better performance on modern hardware.  For 
> common case, this would be a 5.2x boost on FreeBSD/amd64.  The code is 
> intended for MI use when there is no hand-optimized assembly.
> 	http://people.freebsd.org/~delphij/for_review/strlen.diff
> Note that this version of strlen() has suboptimal performance if there
> are a lot of characters that has their highest bit set (we can change 
> it to have uniform performance at the expense of about ~30% 
> performance penalty).
> Comments?

I only glanced over it, but I like the idea about having it.

I see that you investigated this before[1]?  Amusingly, I did something 
similar two years later[2] with a C version of strlen()[3].  :)

Out of curiosity, is an assert (i.e., CTASSERT) better than an #error?

   1. http://lists.freebsd.org/mailman/htdig/freebsd-arch/2005-August/004076.html
   2. http://lists.freebsd.org/pipermail/freebsd-arch/2007-July/006636.html
   3. http://www.farley.org/freebsd/tmp/strlen/strlen.c
scf at FreeBSD.org

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