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Re: [Qemu-devel] [PATCH] hw/audio/fmopl.c: Avoid clang warning about shi
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH] hw/audio/fmopl.c: Avoid clang warning about shifting negative number |
Date: |
Tue, 17 Nov 2015 10:45:38 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 |
On 16/11/2015 16:16, Peter Maydell wrote:
> Newer versions of clang warn:
>
> hw/audio/fmopl.c:1085:39: warning: shifting a negative signed value is
> undefined [-Wshift-negative-value]
> data = Limit( outd[0] , OPL_MAXOUT, OPL_MINOUT );
> ^~~~~~~~~~
> hw/audio/fmopl.c:75:28: note: expanded from macro 'OPL_MINOUT'
> #define OPL_MINOUT (-0x8000<<OPL_OUTSB)
> ~~~~~~~^
>
> Rephrase the definition of OPL_MINOUT to avoid the undefined behaviour.
>
> Signed-off-by: Peter Maydell <address@hidden>
> ---
> hw/audio/fmopl.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/hw/audio/fmopl.c b/hw/audio/fmopl.c
> index 81c0c1b..807b29c 100644
> --- a/hw/audio/fmopl.c
> +++ b/hw/audio/fmopl.c
> @@ -72,7 +72,7 @@ static int opl_dbg_maxchip,opl_dbg_chip;
> /* final output shift , limit minimum and maximum */
> #define OPL_OUTSB (TL_BITS+3-16) /* OPL output final shift 16bit
> */
> #define OPL_MAXOUT (0x7fff<<OPL_OUTSB)
> -#define OPL_MINOUT (-0x8000<<OPL_OUTSB)
> +#define OPL_MINOUT (-(0x8000<<OPL_OUTSB))
Again: let's stop this madness!!!!!!!!!!!!!!!!!!!!!!
(Yes, so many exclamation marks).
This is clearly computing -32768 * 2^N, not -(32768 * 2^N). The latter
is totally, utterly wrong, because 32768 is _not even expressible_ as a
16-bit fixed point value, which OPL_MINOUT/OPL_MAXOUT obviously are.
I'll shortly post a patch to disable this obnoxious warning.
Paolo