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

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Message-ID: <4116142.9TFg0imz4M@ws-140106>
Date:   Thu, 07 Nov 2019 14:54:52 +0100
From:   Alexander Stein <alexander.stein@...tec-electronic.com>
To:     Jonathan Cameron <jic23@...nel.org>
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

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>
> ---
> 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;
> 


-- 
Dipl-Inf. Alexander Stein

SYS TEC electronic AG
Am Windrad 2
08468 Heinsdorfergrund
Germany
Tel: +49-3765-38600-0, Fax: +49-3765-38600-4100
Email   : alexander.stein@...tec-electronic.com
Internet: http://www.systec-electronic.com

Board of Directors: Dipl.-Ing. Ronald Sieber, Dipl.-Ing. Dirk Bause
Chairman of the Supervisory Board: Dipl.-Phys. Siegmar Schmidt
Commercial registry: Amtsgericht Chemnitz, HRB 32220; USt.-Id Nr. 
DE150534010

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