On 31/10/14 18:43, Hartmut Knaack wrote:
> Vlad Dogaru schrieb am 31.10.2014 12:44:
>> On Fri, Oct 31, 2014 at 02:23:33AM +0100, Hartmut Knaack wrote:
>>> The calculations for temperature and pressure compensation were already slightly
>>> optimized in comparison to the data sheet. So, it makes sense to optimize even a
>>> bit more, making proper use of C operators:
>>> - variable t in bmp280_compensate_temp() can be eliminated by directly
>>> returning the result of the relevant equation.
>>> - make use of the += operator, eliminate an unnecessary parenthesis level and
>>> directly return the result of the last equation in
>>> bmp280_compensate_press().
>>> When the initialization of the ctrl_meas register fails, the error message will
>>> now mention the right register name.
>>> During probe, i2c_set_clientdata() is called, although it is not necessary. Drop
>>> it.
>>>
>>> Signed-off-by: Hartmut Knaack <knaack.h@xxxxxx>
>>> ---
>>> diff --git a/drivers/iio/pressure/bmp280.c b/drivers/iio/pressure/bmp280.c
>>> index 75038da..4f6ae4d 100644
>>> --- a/drivers/iio/pressure/bmp280.c
>>> +++ b/drivers/iio/pressure/bmp280.c
>>> @@ -200,7 +200,7 @@ static s32 bmp280_compensate_temp(struct bmp280_data *data,
>>> struct bmp280_comp_temp *comp,
>>> s32 adc_temp)
>>> {
>>> - s32 var1, var2, t;
>>> + s32 var1, var2;
>>>
>>> var1 = (((adc_temp >> 3) - ((s32) comp->dig_t1 << 1)) *
>>> ((s32) comp->dig_t2)) >> 11;
>>> @@ -209,9 +209,7 @@ static s32 bmp280_compensate_temp(struct bmp280_data *data,
>>> ((s32) comp->dig_t3)) >> 14;
>>>
>>> data->t_fine = var1 + var2;
>>> - t = (data->t_fine * 5 + 128) >> 8;
>>> -
>>> - return t;
>>> + return (data->t_fine * 5 + 128) >> 8;
>>
>> Shouldn't the compiler take care of this?
> That would be preferable. I just don't see the real benefit in having the extra step of storing the result (and taking care of an extra variable) before returning it. And I am aware, that this calculation is derived from the one in the data sheet (which looks a bit questionable to me with its unnecessary parenthesis and variable). But since you already started optimizing, it seemed legitimate to consolidate it even a bit more.
I'm with Hartmut on this, no point in having more actual code / local variables than
needed... Just a few more lines of code for no gain :)
>>
>>> }
>>>
>>> /*
>>> @@ -229,11 +227,11 @@ static u32 bmp280_compensate_press(struct bmp280_data *data,
>>>
>>> var1 = ((s64) data->t_fine) - 128000;
>>> var2 = var1 * var1 * (s64) comp->dig_p6;
>>> - var2 = var2 + ((var1 * (s64) comp->dig_p5) << 17);
>>> - var2 = var2 + (((s64) comp->dig_p4) << 35);
>>> + var2 += ((var1 * (s64) comp->dig_p5) << 17);
>>> + var2 += (((s64) comp->dig_p4) << 35);
>>> var1 = ((var1 * var1 * (s64) comp->dig_p3) >> 8) +
>>> ((var1 * (s64) comp->dig_p2) << 12);
>>> - var1 = (((((s64) 1) << 47) + var1)) * ((s64) comp->dig_p1) >> 33;
>>> + var1 = ((((s64) 1) << 47) + var1) * ((s64) comp->dig_p1) >> 33;
>>>
>>> if (var1 == 0)
>>> return 0;
>>> @@ -242,9 +240,7 @@ static u32 bmp280_compensate_press(struct bmp280_data *data,
>>> p = div64_s64(p, var1);
>>> var1 = (((s64) comp->dig_p9) * (p >> 13) * (p >> 13)) >> 25;
>>> var2 = (((s64) comp->dig_p8) * p) >> 19;
>>> - p = ((p + var1 + var2) >> 8) + (((s64) comp->dig_p7) << 4);
>>> -
>>> - return (u32) p;
>>> + return (u32)((p + var1 + var2) >> 8) + (((s64) comp->dig_p7) << 4);
>>
>> And this?
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>
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