Hi!
> From: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
>
> With some high resolution sensors such as the ad7746 the
> build up of error when multiplying the _raw and _scale
> values together can be significant. Reduce this affect by
> providing additional resolution in both calculation and
> formatting of result.
>
> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
> ---
> drivers/iio/industrialio-core.c | 23 +++++++++++++++--------
> 1 file changed, 15 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> index 2f48e9a97274..d831835770da 100644
> --- a/drivers/iio/industrialio-core.c
> +++ b/drivers/iio/industrialio-core.c
> @@ -683,14 +683,21 @@ static ssize_t __iio_format_value(char *buf, size_t offset, unsigned int type,
> else
> return sysfs_emit_at(buf, offset, "%d.%09u", tmp0,
> abs(tmp1));
> - case IIO_VAL_FRACTIONAL_LOG2:
> - tmp2 = shift_right((s64)vals[0] * 1000000000LL, vals[1]);
> - tmp0 = (int)div_s64_rem(tmp2, 1000000000LL, &tmp1);
> - if (tmp0 == 0 && tmp2 < 0)
> - return sysfs_emit_at(buf, offset, "-0.%09u", abs(tmp1));
> - else
> - return sysfs_emit_at(buf, offset, "%d.%09u", tmp0,
> - abs(tmp1));
> + case IIO_VAL_FRACTIONAL_LOG2: {
> + u64 t1, t2;
> + int integer;
> + bool neg = vals[0] < 0;
> +
> + t1 = shift_right((u64)abs(vals[0]) * 1000000000000ULL, vals[1]);
While the multiplication is safe if val[0] is 24 bits or less, I
wonder if that's OK for *all* the existing stuff? I would have guessed
that something somewhere needs more bits than that? Did you consider the
rescaler? And if everything currently really does fit in 24 bits, do we
really want to make it difficult to add something beyond 24 bits later
on?
Cheers,
Peter
> + integer = (int)div64_u64_rem(t1, 1000000000000ULL, &t2);
> + if (integer == 0 && neg)
> + return sysfs_emit_at(buf, offset, "-0.%012llu", abs(t2));
> + if (neg)
> + integer *= -1;
> + return sysfs_emit_at(buf, offset, "%d.%012llu", integer,
> + abs(t2));
> + }
> + }
> case IIO_VAL_INT_MULTIPLE:
> {
> int i;
> --
> 2.35.3
>
