4x faster strlen with 4 char sentinel
qznc via Digitalmars-d-announce
digitalmars-d-announce at puremagic.com
Tue Jun 28 02:18:34 PDT 2016
On Sunday, 26 June 2016 at 16:40:08 UTC, Jay Norwood wrote:
> After watching Andre's sentinel thing, I'm playing with strlen
> on char strings with 4 terminating 0s instead of a single one.
> Seems to work and is 4x faster compared to the runtime version.
>
> nothrow pure size_t strlen2(const(char)* c) {
> if (c is null)
> return 0;
> size_t l=0;
> while (*c){ c+=4; l+=4;}
> while (*c==0){ c--; l--;}
> return l+1;
> }
>
> This is the timing of my test case, which I can post if anyone
> is interested.
> strlen\Release>strlen
> 2738
> 681
Did you also compare to strlen from libc? I'd guess GNU libc uses
a lot more tricks like vector instructions.
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