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

[Philippe Mathieu-Daudé]

On 5/28/20 10:57 AM, Thomas Huth wrote:
> 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.

I first wrote

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

But then thought this would diverge from Eric suggestion, so I kept what
he wrote (which is a bit closer to the style of rest of this file).

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

Thanks!