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iio: afe: rescale: fix accuracy for small fractional scales

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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>
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>
This commit is contained in:
Liam Beguin 2022-02-12 21:57:33 -05:00 committed by Jonathan Cameron
parent a29c328365
commit f5fc003d48
1 changed files with 17 additions and 3 deletions
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20
drivers/iio/afe/iio-rescale.c
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@ -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;