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| author | Liam Beguin <liambeguin@gmail.com> | 2022-02-12 21:57:33 -0500 |
|---|---|---|
| committer | Jonathan Cameron <Jonathan.Cameron@huawei.com> | 2022-02-27 13:38:16 +0000 |
| commit | f5fc003d48033559314f1c9de8198f58f14ed557 (patch) | |
| tree | 40f62414836f50503b083c7113ebe3777631b47a /drivers/iio | |
| parent | a29c3283653b80b916c5ca5292c5d36415e38e92 (diff) | |
| download | linux-stable-f5fc003d48033559314f1c9de8198f58f14ed557.tar.gz linux-stable-f5fc003d48033559314f1c9de8198f58f14ed557.tar.bz2 linux-stable-f5fc003d48033559314f1c9de8198f58f14ed557.zip | |
iio: afe: rescale: fix accuracy for small fractional scales
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>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20220213025739.2561834-5-liambeguin@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Diffstat (limited to 'drivers/iio')
| -rw-r--r-- | drivers/iio/afe/iio-rescale.c | 20 |
1 files changed, 17 insertions, 3 deletions
diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c index 8eaf766e28cc..5d78f0cf47d2 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 ? 1000000000L : 1000000L; |