linux-kernel - Re: [PATCH] NTFS: Change string pointers to string constants.

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Date:	Wed, 09 Dec 2009 16:07:50 +0100
From:	walter harms <wharms@....de>
To:	Marcin Slusarz <marcin.slusarz@...il.com>
Cc:	Joe Perches <joe@...ches.com>,
	Anton Altaparmakov <aia21@....ac.uk>,
	John Daiker <daikerjohn@...il.com>,
	kernel-janitors@...r.kernel.org, aia21@...tab.net,
	linux-ntfs-dev@...ts.sourceforge.net,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] NTFS: Change string pointers to string constants.



Marcin Slusarz schrieb:
> On Mon, Dec 07, 2009 at 05:47:13PM -0800, Joe Perches wrote:
>> On Tue, 2009-12-08 at 00:57 +0000, Anton Altaparmakov wrote:
>>> Can you please explain the rational for making this change?
>> Perhaps it's not worth much, but it saves a pointer reference.
>>
>> $ cat pointer.c
>> #include <string.h>
>> #include <stdio.h>
>>
>> int main (int argc, char** argv)
>> {
>> 	static const char *foo = "abcdefg";
>> 	printf("%s\n", foo);
>> 	return 0;
>> }
>>
>> $ gcc -c pointer.c
>> $ size pointer.o
>>    text	   data	    bss	    dec	    hex	filename
>>      37	      4	      0	     41	     29	pointer.o
>>
>> $ cat reference.c
>> #include <string.h>
>> #include <stdio.h>
>>
>> int main (int argc, char** argv)
>> {
>> static const char foo[] = "abcdefg";
>> printf("%s\n", foo);
>> return 0;
>> }
>>
>> $ gcc -c reference.c
>> $ size reference.o
>>    text    data     bss     dec     hex filename
>>      36       0       0      36      24 reference.o
> 
> Yeah, for static variables it's better. But for automatic variables
> it's worse, because it now has to do a copy at runtime.
> And the patch changes both types.
> 
> $ size pointer.o reference.o
>    text    data     bss     dec     hex filename
>     101       8       0     109      6d pointer.o
>      96       0       0      96      60 reference.o
> 
> $ size pointer-nonstatic.o reference-nonstatic.o
>    text    data     bss     dec     hex filename
>     106       0       0     106      6a pointer-nonstatic.o
>     109       0       0     109      6d reference-nonstatic.o
> --


nobody should spend to much time on this. gcc <what ever next version>
will have different results. It is better to spend time improving
the compiler and make it generate shorter/faster code.

just my 2 cents,
 wh
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