linux-kernel - Re: [PATCH v2 1/1] iio: core: Fix fractional format generation

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Date:   Sat, 9 Nov 2019 11:55:19 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Alexander Stein <alexander.stein@...tec-electronic.com>
Cc:     Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/1] iio: core: Fix fractional format generation

On Thu, 07 Nov 2019 14:54:52 +0100
Alexander Stein <alexander.stein@...tec-electronic.com> wrote:

> Gentle ping
> 
> On Thursday, August 22, 2019, 8:06:07 AM CET 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.
> > 
> > Signed-off-by: Alexander Stein <alexander.stein@...tec-electronic.com>

Apologies. I'd missed this v2 entirely for some reason.

It looks correct to me, but as Lars had inputs on v1...

Lars, could you take a quick look at this v2 and give an ack if
you are happy with it.

Thanks,

Jonathan

> > ---
> > Changes in v2:
> > * Support vals[0] >= and vals[1] < 0 in IIO_VAL_FRACTIONAL
> > * Note: IIO_VAL_FRACTIONAL is untested, as I lack hardware
> > * Note2: Currently IIO_VAL_FRACTIONAL is only called with vals[1] from
> >          in-kernel drivers AFAICS
> > 
> >  drivers/iio/industrialio-core.c | 11 +++++++++--
> >  1 file changed, 9 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> > index 245b5844028d..247338142c87 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;
> > +	char *sign;
> >  	bool scale_db = false;
> >  
> >  	switch (type) {
> > @@ -593,11 +594,17 @@ 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));
> > +		if (vals[1] < 0) {
> > +			sign = vals[0] >= 0 ? "-" : "";
> > +		} else {
> > +			sign = vals[0] < 0 ? "-" : "";
> > +		}
> > +		return snprintf(buf, len, "%s%u.%09u", sign, abs(tmp0), abs(tmp1));
> >  	case IIO_VAL_FRACTIONAL_LOG2:
> > +		sign = vals[0] < 0 ? "-" : "";
> >  		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;
> >   
> 
>