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

[Justin Madru]

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@xxxxxxxxx>
>
> regards,
> dan carpenter
>
>    
> > Signed-off-by: Justin Madru<jdm64@xxxxxxxxx>
> > ---
> >   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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