From: "Jörg Krause" <joerg.krause@embedded.rocks>
To: Clemens Ladisch <clemens@ladisch.de>, alsa-devel@alsa-project.org
Subject: Re: [PATCH] pcm: softvol: fix signedness of tlv data type
Date: Sun, 08 May 2016 20:18:19 +0200 [thread overview]
Message-ID: <1462731499.2641.3.camel@embedded.rocks> (raw)
In-Reply-To: <38c794bd-5eda-2bb2-7022-a13e2869dc3a@ladisch.de>
Hello,
On Sa, 2016-05-07 at 09:06 +0200, Clemens Ladisch wrote:
> Jörg Krause wrote:
> > For the softvol plugin the TLV data are written wrong, e.g. for the
> > default values
> > of min_dB = -51 dB and max_dB = 0 dB, alsactl generates the
> > following state:
> >
> > tlv '00000001000000080000000000000014'
> >
> > As both min_dB and max_dB can be negative numbers, the tlv type
> > must not be
> > unsigned.
>
> TLVs always are unsigned. But they can contain bit patterns that are
> to
> be interpreted as signed.
I see!
> > - unsigned int tlv[4];
> > + int tlv[4];
> > tlv[0] = SND_CTL_TLVT_DB_SCALE;
> > tlv[1] = 2 * sizeof(int);
> > tlv[2] = svol->min_dB * 100;
>
> The problem is that conversion of a negative floating-point number
> into
> an unsigned integer results in undefined behaviour, and on your
> architecture (whatever it is), this results in zero.
>
> The correct way to handle this would be something like this:
>
> tlv[i] = (int)(...);
This fixes the issue for my ARM target, many thanks! I'll send an
updated version.
Many thanks for the review!
Best regards,
Jörg Krause
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prev parent reply other threads:[~2016-05-08 18:18 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-06 21:08 [PATCH] pcm: softvol: fix signedness of tlv data type Jörg Krause
2016-05-07 7:06 ` Clemens Ladisch
2016-05-08 18:18 ` Jörg Krause [this message]
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