Re: [PATCH v2] fpu/softfloat: Silent 'bitwise negation of a boolean expression' warning

[Thomas Huth]

On 28/05/2020 10.48, Philippe Mathieu-Daudé wrote:
> When building with clang version 10.0.0-4ubuntu1, we get:
> 
>     CC      lm32-softmmu/fpu/softfloat.o
>   fpu/softfloat.c:3365:13: error: bitwise negation of a boolean expression; 
> did you mean logical negation? [-Werror,-Wbool-operation]
>       absZ &= ~ ( ( ( roundBits ^ 0x40 ) == 0 ) & roundNearestEven );
>               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
>   fpu/softfloat.c:3423:18: error: bitwise negation of a boolean expression; 
> did you mean logical negation? [-Werror,-Wbool-operation]
>           absZ0 &= ~ ( ( (uint64_t) ( absZ1<<1 ) == 0 ) & roundNearestEven );
>                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
>   fpu/softfloat.c:3483:18: error: bitwise negation of a boolean expression; 
> did you mean logical negation? [-Werror,-Wbool-operation]
>           absZ0 &= ~(((uint64_t)(absZ1<<1) == 0) & roundNearestEven);
>                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
>   fpu/softfloat.c:3606:13: error: bitwise negation of a boolean expression; 
> did you mean logical negation? [-Werror,-Wbool-operation]
>       zSig &= ~ ( ( ( roundBits ^ 0x40 ) == 0 ) & roundNearestEven );
>               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
>   fpu/softfloat.c:3760:13: error: bitwise negation of a boolean expression; 
> did you mean logical negation? [-Werror,-Wbool-operation]
>       zSig &= ~ ( ( ( roundBits ^ 0x200 ) == 0 ) & roundNearestEven );
>               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
>   fpu/softfloat.c:3987:21: error: bitwise negation of a boolean expression; 
> did you mean logical negation? [-Werror,-Wbool-operation]
>                       ~ ( ( (uint64_t) ( zSig1<<1 ) == 0 ) & roundNearestEven 
> );
>                       
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
>   fpu/softfloat.c:4003:22: error: bitwise negation of a boolean expression; 
> did you mean logical negation? [-Werror,-Wbool-operation]
>               zSig0 &= ~ ( ( (uint64_t) ( zSig1<<1 ) == 0 ) & 
> roundNearestEven );
>                        
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
>   fpu/softfloat.c:4273:18: error: bitwise negation of a boolean expression; 
> did you mean logical negation? [-Werror,-Wbool-operation]
>           zSig1 &= ~ ( ( zSig2 + zSig2 == 0 ) & roundNearestEven );
>                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Fix by rewriting the fishy bitwise AND of two bools as an int.
> 
> Suggested-by: Eric Blake <eblake@redhat.com>
> Buglink: https://bugs.launchpad.net/bugs/1881004
> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> ---
> v2: Resend without the Cc: "Toni Wilen <twilen@winuae.net>" tag
> ---
>  fpu/softfloat.c | 33 ++++++++++++++++++++++++---------
>  1 file changed, 24 insertions(+), 9 deletions(-)
> 
> diff --git a/fpu/softfloat.c b/fpu/softfloat.c
> index 6c8f2d597a..0dd57eddd7 100644
> --- a/fpu/softfloat.c
> +++ b/fpu/softfloat.c
> @@ -3362,7 +3362,9 @@ static int32_t roundAndPackInt32(bool zSign, uint64_t 
> absZ,
>      }
>      roundBits = absZ & 0x7F;
>      absZ = ( absZ + roundIncrement )>>7;
> -    absZ &= ~ ( ( ( roundBits ^ 0x40 ) == 0 ) & roundNearestEven );
> +    if (((roundBits ^ 0x40) == 0) && roundNearestEven) {
> +        absZ &= ~1;
> +    }

You could get rid of some more parentheses now:

   if ((roundBits ^ 0x40) == 0 && roundNearestEven)

... also in the other hunks.

Anyway:
Reviewed-by: Thomas Huth <thuth@redhat.com>