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Mon, 31 Aug 2020 08:55:26 +0000 From: Anand Ashok Dumbre To: Jonathan Cameron CC: "knaack.h@gmx.de" , "lars@metafoo.de" , "pmeerw@pmeerw.net" , Michal Simek , git , "linux-iio@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" Subject: RE: [PATCH v2] iio: core: Fix IIO_VAL_FRACTIONAL calculation for negative values Thread-Topic: [PATCH v2] iio: core: Fix IIO_VAL_FRACTIONAL calculation for negative values Thread-Index: AQHWe9Uy2J6wql2dV0mNnaIWIGIkoqlPN8YAgAK0ytA= Date: Mon, 31 Aug 2020 08:55:26 +0000 Message-ID: References: <1598465676-28912-1-git-send-email-anand.ashok.dumbre@xilinx.com> <20200829161900.713541cd@archlinux> In-Reply-To: <20200829161900.713541cd@archlinux> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-Auto-Response-Suppress: DR, RN, NRN, OOF, AutoReply X-MS-TNEF-Correlator: authentication-results: kernel.org; dkim=none (message not signed) header.d=none;kernel.org; dmarc=none action=none header.from=xilinx.com; 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If you look at the function where this is used, all other IIO_VAL_MICRO and= NANO have this fix added at some point. Thanks, Anand > -----Original Message----- > From: Jonathan Cameron > Sent: Saturday, August 29, 2020 4:19 PM > To: Anand Ashok Dumbre > Cc: knaack.h@gmx.de; lars@metafoo.de; pmeerw@pmeerw.net; Michal > Simek ; git ; linux- > iio@vger.kernel.org; linux-arm-kernel@lists.infradead.org; linux- > kernel@vger.kernel.org; Anand Ashok Dumbre > Subject: Re: [PATCH v2] iio: core: Fix IIO_VAL_FRACTIONAL calculation for > negative values >=20 > On Wed, 26 Aug 2020 11:14:36 -0700 > Anand Ashok Dumbre wrote: >=20 > > Fixes IIO_VAL_FRACTIONAL for case when the result is negative and > > exponent is 0. > > > > example: if the result is -0.75, tmp0 will be 0 and tmp1 =3D 75 This > > causes the output to lose sign because of %d in snprintf which works > > for tmp0 <=3D -1. > > > > Signed-off-by: Anand Ashok Dumbre >=20 > Looks good. Just one last thing. >=20 > Is this actually hit in an existing driver? I'm just wondering how far b= ack we > need to push it in stable etc. >=20 > Thanks, >=20 > Jonathan >=20 > > --- > > changes since v1: > > Changed -%d to -0 to make the fix clearer. > > Removed the email footer. > > Updated the commit description with an example > > -- > > drivers/iio/industrialio-core.c | 8 ++++++-- > > 1 file changed, 6 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/iio/industrialio-core.c > > b/drivers/iio/industrialio-core.c index cdcd16f1..a239fa2 100644 > > --- a/drivers/iio/industrialio-core.c > > +++ b/drivers/iio/industrialio-core.c > > @@ -592,6 +592,7 @@ 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 =3D false; > > > > switch (type) { > > @@ -614,10 +615,13 @@ static ssize_t __iio_format_value(char *buf, > size_t len, unsigned int type, > > else > > return scnprintf(buf, len, "%d.%09u", vals[0], vals[1]); > > case IIO_VAL_FRACTIONAL: > > - tmp =3D div_s64((s64)vals[0] * 1000000000LL, vals[1]); > > + tmp2 =3D div_s64((s64)vals[0] * 1000000000LL, vals[1]); > > tmp1 =3D vals[1]; > > tmp0 =3D (int)div_s64_rem(tmp, 1000000000, &tmp1); > > - return scnprintf(buf, len, "%d.%09u", tmp0, abs(tmp1)); > > + if ((tmp2 < 0) && (tmp0 =3D=3D 0)) > > + return snprintf(buf, len, "-0.%09u", abs(tmp1)); > > + else > > + return snprintf(buf, len, "%d.%09u", tmp0, > abs(tmp1)); > > case IIO_VAL_FRACTIONAL_LOG2: > > tmp =3D shift_right((s64)vals[0] * 1000000000LL, vals[1]); > > tmp0 =3D (int)div_s64_rem(tmp, 1000000000LL, &tmp1);