Re: [PATCH] audio/mixeng: fix clang 10+ warning

From: Gerd Hoffmann <kraxel@redhat.com>
To: "Volker Rümelin" <vr_qemu@t-online.de>
Cc: "Alexander Bulekov" <alxndr@bu.edu>,
	"Richard Henderson" <richard.henderson@linaro.org>,
	"Philippe Mathieu-Daudé" <f4bug@amsat.org>,
	QEMU <qemu-devel@nongnu.org>
Subject: Re: [PATCH] audio/mixeng: fix clang 10+ warning
Date: Tue, 26 May 2020 07:51:10 +0200	[thread overview]
Message-ID: <20200526055110.xhqlolr4l6on2wya@sirius.home.kraxel.org> (raw)
In-Reply-To: <20200523201712.23908-1-vr_qemu@t-online.de>

On Sat, May 23, 2020 at 10:17:12PM +0200, Volker RÃ¼melin wrote:
> The code in CONV_NATURAL_FLOAT() and CLIP_NATURAL_FLOAT()
> seems to use the constant 2^31-0.5 to convert float to integer
> and back. But the float type lacks the required precision and
> the constant used for the conversion is 2^31. This is equiva-
> lent to a [-1.f, 1.f] <-> [INT32_MIN, INT32_MAX + 1] mapping.
> 
> This patch explicitly writes down the used constant. The
> compiler generated code doesn't change.
> 
> The constant 2^31 has an exact float representation and the
> clang 10 compiler stops complaining about an implicit int to
> float conversion with a changed value.
> 
> A few notes:
> - The conversion of 1.f to INT32_MAX + 1 doesn't overflow. The
>   type of the destination variable is int64_t.
> - At a later stage one of the clip_* functions in
>   audio/mixeng_template.h limits INT32_MAX + 1 to the integer
>   range.
> - The clip_natural_float_* functions in audio/mixeng.c convert
>   INT32_MAX and INT32_MAX + 1 to 1.f.
> 
> Buglink: https://bugs.launchpad.net/bugs/1878627
> Signed-off-by: Volker RÃ¼melin <vr_qemu@t-online.de>

Added to audio queue.

thanks,
  Gerd