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> --- 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_ */ -- 2.1.4 -- 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
