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

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Message-ID: <1412523392.2916.3.camel@joe-AO725>
Date:	Sun, 05 Oct 2014 08:36:32 -0700
From:	Joe Perches <joe@...ches.com>
To:	Rickard Strandqvist <rickard_strandqvist@...ctrumdigital.se>
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
Subject: Re: [PATCH] lib: string.c:  A speed optimized for strncpy

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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