linux-kernel - Re: [PATCH] lib: string.c: A speed optimized for strncpy

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Date:	Sun, 5 Oct 2014 18:01:43 +0200
From:	Rickard Strandqvist <rickard_strandqvist@...ctrumdigital.se>
To:	Joe Perches <joe@...ches.com>
Cc:	Grant Likely <grant.likely@...aro.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <ak@...ux.intel.com>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] lib: string.c: A speed optimized for strncpy

Hi

Yes, it can be faster, even if it is as you say, probably a difference
depending on the size of the count.
And even greater need to test this on a variety of hardware :-/

But I try to do my test with the memset variant to.

Kind regards
Rickard Strandqvist


2014-10-05 17:36 GMT+02:00 Joe Perches <joe@...ches.com>:
> On Sun, 2014-10-05 at 15:29 +0200, Rickard Strandqvist wrote:
>> This variant is in my tests about 7-10% faster, and also think
>> it is perhaps even clearer code than before.
> []
>> diff --git a/lib/string.c b/lib/string.c
> []
>> @@ -123,12 +123,12 @@ char *strncpy(char *dest, const char *src, size_t count)
>>  {
>>       char *tmp = dest;
>>
>> -     while (count) {
>> -             if ((*tmp = *src) != 0)
>> -                     src++;
>> -             tmp++;
>> -             count--;
>> -     }
>> +     while (count && (*tmp++ = *src++))
>> +             --count;
>> +
>> +     while (count--)
>> +             *tmp++ = '\0';
>
> Perhaps it could be faster to use memset.
> It might depend on the value of count.
>
> {
>         while (count && (*tmp++ = *src++))
>                 count--;
>
>         if (count > 0)
>                 memset(tmp, 0, count);
> }
>
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