Re: [WIKI] Optimization overview.

[David Miller <davem at davemloft dot net>]

From: Ondřej Bílka <neleai@seznam.cz>
Date: Mon, 18 Feb 2013 18:22:58 +0100

> I wrote about common string optimizations at
> http://sourceware.org/glibc/wiki/Optimizations/string_functions
> I put there control flow that is fastest in practice among those I
> tried (there are several possible tradeoffs which I will write about). 
> I plan use it for most subsequent patches.
> 
> 
> What can be covered relatively generaly?
> Comments?

Thanks for writing this up, it is of great value.

On Sparc v9 32-bit and 64-bit I do the unaligned initial word in
parallel with the loop setup.  This seemed to be the most optimal.

You simply align the pointer and do an aligned load, and use a 'or' to
set all of the bytes in the word up to the actual starting byte to
one.  If the initial pointer is aligned, the mask cancels out and we
pre-process one full word upon entry to the loop.

PowerPC uses this method as well, as that's where I got the idea
from.