Messages in this thread Patch in this message | | | From | Liam Beguin <> | Subject | [PATCH v12 09/16] iio: afe: rescale: fix accuracy for small fractional scales | Date | Sat, 8 Jan 2022 15:53:12 -0500 |
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The approximation caused by integer divisions can be costly on smaller scale values since the decimal part is significant compared to the integer part. Switch to an IIO_VAL_INT_PLUS_NANO scale type in such cases to maintain accuracy.
Signed-off-by: Liam Beguin <liambeguin@gmail.com> Reviewed-by: Peter Rosin <peda@axentia.se> --- drivers/iio/afe/iio-rescale.c | 20 +++++++++++++++++--- 1 file changed, 17 insertions(+), 3 deletions(-)
diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c index 68eb3e341939..ed3ef994997f 100644 --- a/drivers/iio/afe/iio-rescale.c +++ b/drivers/iio/afe/iio-rescale.c @@ -24,7 +24,7 @@ int rescale_process_scale(struct rescale *rescale, int scale_type, int *val, int *val2) { s64 tmp; - s32 rem; + s32 rem, rem2; u32 mult; u32 neg; @@ -43,9 +43,23 @@ int rescale_process_scale(struct rescale *rescale, int scale_type, tmp = (s64)*val * 1000000000LL; tmp = div_s64(tmp, rescale->denominator); tmp *= rescale->numerator; - tmp = div_s64(tmp, 1000000000LL); + + tmp = div_s64_rem(tmp, 1000000000LL, &rem); *val = tmp; - return scale_type; + + if (!rem) + return scale_type; + + tmp = 1 << *val2; + + rem2 = *val % (int)tmp; + *val = *val / (int)tmp; + + *val2 = rem / (int)tmp; + if (rem2) + *val2 += div_s64((s64)rem2 * 1000000000LL, tmp); + + return IIO_VAL_INT_PLUS_NANO; case IIO_VAL_INT_PLUS_NANO: case IIO_VAL_INT_PLUS_MICRO: mult = scale_type == IIO_VAL_INT_PLUS_NANO ? GIGA : MEGA; -- 2.34.0
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