On 05/08/15 14:38, Lars-Peter Clausen wrote: > Add inverse unit conversion macro to convert from standard IIO units to > units that might be used by some devices. > > Those are useful in combination with scale factors that are specified as > IIO_VAL_FRACTIONAL. Typically the denominator for those specifications will > contain the maximum raw value the sensor will generate and the numerator > the value it maps to in a specific unit. Sometimes datasheets specify those > in different units than the standard IIO units (e.g. degree/s instead of > rad/s) and so we need to do a unit conversion. > > From a mathematical point of view it does not make a difference whether we > apply the unit conversion to the numerator or the inverse unit conversion > to the denominator since (x / y) / z = x / (y * z). But as the denominator > is typically a larger value and we are rounding both the numerator and > denominator to integer values using the later method gives us a better > precision (E.g. the relative error is smaller if we round 8000.3 to 8000 > rather than rounding 8.3 to 8). > > This is where in inverse unit conversion macros will be used. > > Signed-off-by: Lars-Peter Clausen <lars@xxxxxxxxxx> Applied and marked for stable given the next patch. > --- > include/linux/iio/iio.h | 17 +++++++++++++++++ > 1 file changed, 17 insertions(+) > > diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h > index f791482..6bcc9537 100644 > --- a/include/linux/iio/iio.h > +++ b/include/linux/iio/iio.h > @@ -645,6 +645,15 @@ int iio_str_to_fixpoint(const char *str, int fract_mult, int *integer, > #define IIO_DEGREE_TO_RAD(deg) (((deg) * 314159ULL + 9000000ULL) / 18000000ULL) > > /** > + * IIO_RAD_TO_DEGREE() - Convert rad to degree > + * @rad: A value in rad > + * > + * Returns the given value converted from rad to degree > + */ > +#define IIO_RAD_TO_DEGREE(rad) \ > + (((rad) * 18000000ULL + 314159ULL / 2) / 314159ULL) > + > +/** > * IIO_G_TO_M_S_2() - Convert g to meter / second**2 > * @g: A value in g > * > @@ -652,4 +661,12 @@ int iio_str_to_fixpoint(const char *str, int fract_mult, int *integer, > */ > #define IIO_G_TO_M_S_2(g) ((g) * 980665ULL / 100000ULL) > > +/** > + * IIO_M_S_2_TO_G() - Convert meter / second**2 to g > + * @ms2: A value in meter / second**2 > + * > + * Returns the given value converted from meter / second**2 to g > + */ > +#define IIO_M_S_2_TO_G(ms2) (((ms2) * 100000ULL + 980665ULL / 2) / 980665ULL) > + > #endif /* _INDUSTRIAL_IO_H_ */ > -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
