[PATCH v7 08/13] iio: afe: rescale: fix precision on fractional log scale
From: Liam Beguin <hidden>
Date: 2021-08-01 19:40:36
Also in:
linux-iio, lkml
Subsystem:
iio subsystem and drivers, iio unit converter, the rest · Maintainers:
Jonathan Cameron, Peter Rosin, Linus Torvalds
From: Liam Beguin <redacted> The IIO_VAL_FRACTIONAL_LOG2 scale type doesn't return the expected scale. Update the case so that the rescaler returns a fractional type and a more precise scale. Signed-off-by: Liam Beguin <redacted> --- drivers/iio/afe/iio-rescale.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-)
diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
index abd7ad73d1ce..e37a9766080c 100644
--- a/drivers/iio/afe/iio-rescale.c
+++ b/drivers/iio/afe/iio-rescale.c@@ -47,12 +47,17 @@ int rescale_process_scale(struct rescale *rescale, int scale_type, *val2 = rescale->denominator; return IIO_VAL_FRACTIONAL; case IIO_VAL_FRACTIONAL_LOG2: - tmp = *val * 1000000000LL; - do_div(tmp, rescale->denominator); - tmp *= rescale->numerator; - do_div(tmp, 1000000000LL); + if (check_mul_overflow(*val, rescale->numerator, (s32 *)&tmp) || + check_mul_overflow(rescale->denominator, (1 << *val2), (s32 *)&tmp2)) { + tmp = (s64)*val * rescale->numerator; + tmp2 = (s64)rescale->denominator * (1 << *val2); + factor = gcd(abs(tmp), abs(tmp2)); + tmp = div_s64(tmp, factor); + tmp2 = div_s64(tmp2, factor); + } *val = tmp; - return scale_type; + *val2 = tmp2; + return IIO_VAL_FRACTIONAL; case IIO_VAL_INT_PLUS_NANO: case IIO_VAL_INT_PLUS_MICRO: if (scale_type == IIO_VAL_INT_PLUS_NANO)
--
2.30.1.489.g328c10930387