linux-kernel - Re: [PATCH] staging: s5k3e2fx.c: reduce complexity by factoring

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Message-ID: <4B26DA90.7090702@gawab.com>
Date:	Mon, 14 Dec 2009 16:38:40 -0800
From:	Justin Madru <jdm64@...ab.com>
To:	gregkh@...e.de
CC:	Dan Carpenter <error27@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: s5k3e2fx.c: reduce complexity by factoring

On 12/09/2009 01:57 AM, Dan Carpenter wrote:
> On Sat, Dec 05, 2009 at 06:03:20PM -0800, Justin Madru wrote:
>    
>> I was style fixing some code when I ran into this code.
>> It seems like the code could be reduced, by factoring the expression.
>> But this results in a very simple expression.
>>
>> Am I assuming something wrong? Or is this a bug in the original code?
>> This doesn't look right because the assignment of s_move[i] has no mention
>> of the loop counter.
>>
>> Justin
>>
>> ------
>>
>> the code was looping, seting s_move[i] to the following calculations
>>
>> if (actual_step>= 0)
>>          s_move[i] = ((((i + 1) * gain + 0x200) - (i * gain + 0x200)) / 0x400);
>> else
>>          s_move[i] = ((((i + 1) * gain - 0x200) - (i * gain - 0x200)) / 0x400);
>>
>> but, by factoring the expression, it can be shown that they both reduce
>> to a very simple expression:
>>
>>          s_move[i] = gain / 0x400;
>>
>>      
> Heh.
>
> Looks like an improvement to me.
>
> If gain were 16 bits instead of 32 I would think the "* 0x400 / 0x400" was
> designed to mask out the highest 10 bits.
>
> Acked-by:  Dan Carpenter<error27@...il.com>
>
> regards,
> dan carpenter
>
>    
>> Signed-off-by: Justin Madru<jdm64@...ab.com>
>> ---
>>   drivers/staging/dream/camera/s5k3e2fx.c |   10 +++-------
>>   1 files changed, 3 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/staging/dream/camera/s5k3e2fx.c b/drivers/staging/dream/camera/s5k3e2fx.c
>> index f0e49be..d205a2d 100644
>> --- a/drivers/staging/dream/camera/s5k3e2fx.c
>> +++ b/drivers/staging/dream/camera/s5k3e2fx.c
>> @@ -1092,14 +1092,10 @@ static int32_t s5k3e2fx_move_focus(int direction, int32_t num_steps)
>>
>>   	actual_step = step_direction * (int16_t)num_steps;
>>   	pos_offset = init_code + s5k3e2fx_ctrl->curr_lens_pos;
>> -	gain = actual_step * 0x400 / 5;
>> +	gain = actual_step / 5;
>>
>> -	for (i = 0; i<= 4; i++) {
>> -		if (actual_step>= 0)
>> -			s_move[i] = ((((i+1)*gain+0x200) - (i*gain+0x200))/0x400);
>> -		else
>> -			s_move[i] = ((((i+1)*gain-0x200) - (i*gain-0x200))/0x400);
>> -	}
>> +	for (i = 0; i<= 4; i++)
>> +		s_move[i] = gain;
>>
>>   	/* Ring Damping Code */
>>   	for (i = 0; i<= 4; i++) {
>> -- 
>> 1.6.5.4
>>
>> --
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>>      

I've yet to see a reply from GregH. Has this patch been misplaced or 
dropped?
Or is the patch no longer valid/correct?

Justin Madru
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