Re: Optimized? strchr implementations.

[Matt Turner <mattst88@gmail.com>]

On Tue, May 26, 2015 at 7:38 AM, Ondřej Bílka <neleai@seznam.cz> wrote:
> On Tue, May 26, 2015 at 01:23:36PM +0100, Wilco Dijkstra wrote:
>> > Ondřej Bílka wrote:
>> > On Sun, May 24, 2015 at 06:32:14PM +0200, Ondřej Bílka wrote:
>> > > Hi,
>> > > this is nontrivial optimization of string inlines.
>> > > First it decreases icache pressure as you don't need strchr.
>>
>> It's not obvious to me that is the right thing to do. Generally it is best
>> to use the standard C90/C99 functions rather than infrequently used
>> non-standard ones. A quick grep of GLIBC shows strchr is used a lot more
>> than strchrnul, and 9 targets have an optimized strchr vs 5 for strchrnul.
>>
> I looked at how architectures optimize strchr and that number is less.
>
> Some of these are not optimized implementations. If you do gcc
> string/strchr.c -S then you get assembly implementation. Several
> architectures don't exploit any hardware capabilities, just use same
> algorithm as generic so these could be deleted.
>
> I know that generic implementation could be improved and will post a
> patches.
>
> Only two that are real optimizations and don't have strchnul are armv6
> and alpha
> So could you adapt armv6 one?
>
> Richard as you added alpha could you adapt it to strchnul? And why you
> do a binary search there? Accoring to wiki alpha supports ctlz
> instruction that does exactly that.

It's because Alphas < EV67 don't have ctlz.