Re: [PATCH] iio: Fixed IIO_VAL_FRACTIONAL calcuation for negative values

From: Jonathan Cameron
Date: Sat Aug 22 2020 - 06:58:07 EST


On Thu, 20 Aug 2020 11:09:44 -0700
Anand Ashok Dumbre <anand.ashok.dumbre@xxxxxxxxxx> wrote:

> This patch fixes IIO_VAL_FRACTIONAL calculation for negative
> values where the exponent is 0.
>
> Signed-off-by: Anand Ashok Dumbre <anand.ashok.dumbre@xxxxxxxxxx>
Hi,

I would thrown in an example for this description.
Also useful to know if there is a existing driver that is broken
and hence we need to backport this.
If that is the case, please try to figure out an appropriate fixes
tag.

Comments inline + the email footer issue needs sorting out.

Thanks,

Jonathan

> ---
> drivers/iio/industrialio-core.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> index f72c2dc..cd43b17 100644
> --- a/drivers/iio/industrialio-core.c
> +++ b/drivers/iio/industrialio-core.c
> @@ -554,6 +554,7 @@ static ssize_t __iio_format_value(char *buf, size_t len, unsigned int type,
> {
> unsigned long long tmp;
> int tmp0, tmp1;
> + s64 tmp2;
> bool scale_db = false;
>
> switch (type) {
> @@ -576,10 +577,13 @@ static ssize_t __iio_format_value(char *buf, size_t len, unsigned int type,
> else
> return snprintf(buf, len, "%d.%09u", vals[0], vals[1]);
> case IIO_VAL_FRACTIONAL:
> - tmp = div_s64((s64)vals[0] * 1000000000LL, vals[1]);
> + tmp2 = div_s64((s64)vals[0] * 1000000000LL, vals[1]);
> tmp1 = vals[1];
> - tmp0 = (int)div_s64_rem(tmp, 1000000000, &tmp1);
> - return snprintf(buf, len, "%d.%09u", tmp0, abs(tmp1));
> + tmp0 = (int)div_s64_rem(tmp2, 1000000000, &tmp1);
> + if ((tmp2 < 0) && (tmp0 == 0))
> + return snprintf(buf, len, "-%d.%09u", tmp0, abs(tmp1));

Given tmp0 == 0, this might be clearer as
return snprintf(buf, len, "-0.%09u", abs(tmp1));

> + else
> + return snprintf(buf, len, "%d.%09u", tmp0, abs(tmp1));
> case IIO_VAL_FRACTIONAL_LOG2:
> tmp = shift_right((s64)vals[0] * 1000000000LL, vals[1]);
> tmp0 = (int)div_s64_rem(tmp, 1000000000LL, &tmp1);
> --
> 2.7.4
>
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As Andy said, this footer is a problem...