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From: Michael Buesch <mb@bu3sch.de>
To: =?utf-8?q?Rafa=C5=82_Mi=C5=82ecki?= <zajec5@gmail.com>
Subject: Re: [PATCH 3/6] b43: N-PHY: add RSSI calculation for PHY rev < 3
Date: Mon, 11 Jan 2010 23:13:25 +0100
Cc: bcm43xx-dev@lists.berlios.de,
	"linux-wireless@vger.kernel.org" <linux-wireless@vger.kernel.org>,
	"John W. Linville" <linville@tuxdriver.com>
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On Monday 11 January 2010 22:13:31 Rafał Miłecki wrote:
> 2010/1/10 Michael Buesch <mb@bu3sch.de>:
> > On Sunday 10 January 2010 23:13:34 Rafał Miłecki wrote:
> >> +     s32 results_min[4];
> >> +     u8 vcm_final[4];
> >> +     s32 results[4][4];
> >> +     s32 miniq[4][2];
> >> +     memset(results_min, 0, sizeof(s32) * 4);
> >> +     memset(vcm_final, 0, sizeof(u8) * 4);
> >> +     memset(results, 0, sizeof(s32) * 4 * 4);
> >> +     memset(miniq, 0, sizeof(s32) * 4 * 2);
> >
> > Just initialize the variables to zero instead of doing a memset:
> >
> > +       s32 results_min[4] = { 0, };
> > +       u8 vcm_final[4] = { 0, };
> > +       s32 results[4][4] = { 0, };
> > +       s32 miniq[4][2] = { 0, };
> 
> Nice trick, thanks :) Just for two-dimensional arrays I'll have to hack it to:
> s32 results[4][4] = { { 0, }, { 0, }, { 0, }, { 0, } };
> I believe.

No I don't think so.
It's C standard that uninitialized elements on automatic variables are initialized
to zero, _if_ at least one element is initialized to something.
So if you init one element to 0, all others will be 0, too.
I think that should also work for multidimensional arrays. So my example
s32 results[4][4] = { 0, };
should do the right thing. Am I wrong?

Here's a test-program:


mb@maggie:~$ cat t.c
#include <stdio.h>
#include <stdint.h>

int main(void)
{
        int i, j;
        int32_t results[4][4]
#ifdef INIT_IT
= { 0, };
#else
;
#endif

        for (i = 0; i < 4; i++)
                for (j = 0; j < 4; j++)
                        printf("%d\n", results[i][j]);

}
mb@maggie:~$ gcc -o t t.c
mb@maggie:~$ ./t
0
0
0
1
-1077483840
0
0
0
-1077483824
268436224
268536212
0
-1077483776
268436888
268353524
0
mb@maggie:~$ gcc -D INIT_IT -o t t.c
mb@maggie:~$ ./t
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

-- 
Greetings, Michael.