From: Liam Beguin <liambeguin@gmail.com>
To: liambeguin@gmail.com, peda@axentia.se, jic23@kernel.org, lars@metafoo.de
Cc: linux-kernel@vger.kernel.org, linux-iio@vger.kernel.org,
devicetree@vger.kernel.org, robh+dt@kernel.org
Subject: [PATCH v10 08/14] iio: afe: rescale: fix accuracy for small fractional scales
Date: Sun, 19 Dec 2021 17:39:47 -0500 [thread overview]
Message-ID: <20211219223953.16074-9-liambeguin@gmail.com> (raw)
In-Reply-To: <20211219223953.16074-1-liambeguin@gmail.com>
From: Liam Beguin <lvb@xiphos.com>
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 <lvb@xiphos.com>
---
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 e3680998565e..66306477aeab 100644
--- a/drivers/iio/afe/iio-rescale.c
+++ b/drivers/iio/afe/iio-rescale.c
@@ -23,7 +23,7 @@ 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;
@@ -42,9 +42,23 @@ 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 ? NANO : MICRO;
--
2.34.0
next prev parent reply other threads:[~2021-12-19 22:40 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-19 22:39 [PATCH v10 00/14] iio: afe: add temperature rescaling support Liam Beguin
2021-12-19 22:39 ` [PATCH v10 01/14] iio: inkern: apply consumer scale on IIO_VAL_INT cases Liam Beguin
2021-12-19 22:39 ` [PATCH v10 02/14] iio: inkern: apply consumer scale when no channel scale is available Liam Beguin
2021-12-19 22:39 ` [PATCH v10 03/14] iio: inkern: make a best effort on offset calculation Liam Beguin
2021-12-21 5:42 ` Andy Shevchenko
2021-12-21 17:50 ` Liam Beguin
2021-12-19 22:39 ` [PATCH v10 04/14] iio: afe: rescale: expose scale processing function Liam Beguin
[not found] ` <CAHp75VdfPf6FMvkGqhhQg5e5XE1cgE-K8seobe5n0yGarnPGtQ@mail.gmail.com>
2021-12-21 5:43 ` Andy Shevchenko
2021-12-22 2:28 ` Liam Beguin
2021-12-19 22:39 ` [PATCH v10 05/14] iio: afe: rescale: add INT_PLUS_{MICRO,NANO} support Liam Beguin
2021-12-19 22:39 ` [PATCH v10 06/14] iio: afe: rescale: add offset support Liam Beguin
2021-12-19 22:39 ` [PATCH v10 07/14] iio: afe: rescale: use s64 for temporary scale calculations Liam Beguin
2021-12-19 22:39 ` Liam Beguin [this message]
2021-12-19 22:39 ` [PATCH v10 09/14] iio: afe: rescale: reduce risk of integer overflow Liam Beguin
2021-12-19 22:39 ` [PATCH v10 10/14] iio: test: add basic tests for the iio-rescale driver Liam Beguin
2021-12-21 7:09 ` kernel test robot
2021-12-21 8:03 ` kernel test robot
2021-12-19 22:39 ` [PATCH v10 11/14] iio: afe: rescale: add RTD temperature sensor support Liam Beguin
2021-12-19 22:39 ` [PATCH v10 12/14] iio: afe: rescale: add temperature transducers Liam Beguin
2021-12-19 22:39 ` [PATCH v10 13/14] dt-bindings: iio: afe: add bindings for temperature-sense-rtd Liam Beguin
2021-12-19 22:39 ` [PATCH v10 14/14] dt-bindings: iio: afe: add bindings for temperature transducers Liam Beguin
2021-12-20 21:37 ` [PATCH v10 00/14] iio: afe: add temperature rescaling support Peter Rosin
2021-12-22 3:29 ` Liam Beguin
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