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Date: Tue, 16 Jun 2015 13:43:43 +0200
From: Richard Weinberger <richard@nod.at>
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To: Alexey Dobriyan <adobriyan@gmail.com>
CC: lukes357@gmail.com, Linux Kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] small update for strlen, strnlen, use less cpu instructions
References: <CACVxJT-rvN-NX-Z+Eby9uYkubka9_a5ZnEPCBcRT6FRwdVZW3Q@mail.gmail.com>
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Am 16.06.2015 um 13:41 schrieb Alexey Dobriyan:
>> Now strlen() increments a variable for each character it faces,
>> hence it will consume more cycles.
> 
> It doesn't matter if there is a dependency in a loop:
> 
> Before:
>  520:   48 83 c0 01             add    $0x1,%rax
>  524:   80 38 00                cmpb   $0x0,(%rax)
>  527:   75 f7                   jne    520
> 
> After:
>  500:   48 83 c0 01             add    $0x1,%rax
>  504:   80 3c 07 00             cmpb   $0x0,(%rdi,%rax,1)
>  508:   75 f6                   jne    500
> 

Hmmm.
Thanks for pointing this out!

Thanks,
//richard