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

Date: Fri Dec 18 2009 - 18:57:41 EST

On 12/18/2009 10:41 AM, Greg KH wrote:

On Tue, Dec 15, 2009 at 12:52:10PM -0800, Justin Madru wrote:
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, this code redues to the expression
s_move[i] = gain>> 10;

The reason for the complexity was to generate a step function with
integer division and rounding to land on specific values. But these calculations
can be simplified to the following code:

gain = ((actual_step<< 10) / 5)>> 10;
for (i = 0; i<= 4; i++)
s_move[i] = gain;

Care to resend this with a Signed-off-by: line, and add the reviewed-by
line that was requested by Ray?

thanks,

greg k-h
Sorry about that, new at submitting patches, don't completely know the flow yet.
Does the below format work for you? Hopefully my email client won't mess the patch up.

------

Date: Tue, 15 Dec 2009 12:27:31 -0800
Subject: [PATCH] staging: s5k3e2fx.c: simplify complexity by factoring

the code was looping, setting 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, this code reduces to the expression
s_move[i] = gain>> 10;

The reason for the complexity was to generate a step function with
integer division and rounding to land on specific values. But these calculations
can be simplified to the following code:

gain = ((actual_step<< 10) / 5)>> 10;
for (i = 0; i<= 4; i++)
s_move[i] = gain;

Reviewed-by: Ray Lee<ray-lk@xxxxxxxxxxxxx>
---
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..93162a0 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<< 10) / 5)>> 10;

- 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++) {
--
1.6.5.6

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