2019-08-21 17:40:10

by Alexander Stein

Subject: [PATCH 1/1] iio: core: Fix fractional format generation

In case the result is -0.3252 tmp0 is 0 after the div_s64_rem, so tmp0 is
non-negative which results in an output of 0.3252.
Fix this by explicitly handling the negative sign ourselves.

Signed-off-by: Alexander Stein <[email protected]>
---
drivers/iio/industrialio-core.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
index 245b5844028d..18350c1959ae 100644
--- a/drivers/iio/industrialio-core.c
+++ b/drivers/iio/industrialio-core.c
@@ -568,6 +568,7 @@ static ssize_t __iio_format_value(char *buf, size_t len, unsigned int type,
{
unsigned long long tmp;
int tmp0, tmp1;
+ const char *sign = vals[0] < 0 ? "-" : "";
bool scale_db = false;

switch (type) {
@@ -593,11 +594,11 @@ static ssize_t __iio_format_value(char *buf, size_t len, unsigned int type,
tmp = 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));
+ return snprintf(buf, len, "%s%u.%09u", sign, abs(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);
- return snprintf(buf, len, "%d.%09u", tmp0, abs(tmp1));
+ return snprintf(buf, len, "%s%u.%09u", sign, abs(tmp0), abs(tmp1));
case IIO_VAL_INT_MULTIPLE:
{
int i;
--
2.23.0

2019-08-21 20:11:11

by Lars-Peter Clausen

Subject: Re: [PATCH 1/1] iio: core: Fix fractional format generation

On 8/21/19 5:50 PM, Alexander Stein wrote:
> In case the result is -0.3252 tmp0 is 0 after the div_s64_rem, so tmp0 is
> non-negative which results in an output of 0.3252.
> Fix this by explicitly handling the negative sign ourselves.

Hi,

Thanks for you patch. Some comments inline.

>
> Signed-off-by: Alexander Stein <[email protected]>
> ---
> drivers/iio/industrialio-core.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> index 245b5844028d..18350c1959ae 100644
> --- a/drivers/iio/industrialio-core.c
> +++ b/drivers/iio/industrialio-core.c
> @@ -568,6 +568,7 @@ static ssize_t __iio_format_value(char *buf, size_t len, unsigned int type,
> {
> unsigned long long tmp;
> int tmp0, tmp1;
> + const char *sign = vals[0] < 0 ? "-" : "";
> bool scale_db = false;
>
> switch (type) {
> @@ -593,11 +594,11 @@ static ssize_t __iio_format_value(char *buf, size_t len, unsigned int type,
> tmp = 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));
> + return snprintf(buf, len, "%s%u.%09u", sign, abs(tmp0), abs(tmp1));

I think this breaks the case where vals[1] is negative, but vals[0] is
positive. Maybe we can use a similar approach as for
IIO_VAL_INT_PLUS_NANO. Maybe even put this into a small helper function.

> case IIO_VAL_FRACTIONAL_LOG2:
> tmp = shift_right((s64)vals[0] * 1000000000LL, vals[1]);
> tmp0 = (int)div_s64_rem(tmp, 1000000000LL, &tmp1);
> - return snprintf(buf, len, "%d.%09u", tmp0, abs(tmp1));
> + return snprintf(buf, len, "%s%u.%09u", sign, abs(tmp0), abs(tmp1));
> case IIO_VAL_INT_MULTIPLE:
> {
> int i;
>