Re: [PATCH 1/2] hw/dma: sifive_pdma: Improve code readability for "!!foo & bar"

[Philippe Mathieu-Daudé]

On 9/27/21 06:47, Philippe Mathieu-Daudé wrote:
> On 9/27/21 04:21, Bin Meng wrote:
>> GCC seems to be strict about processing pattern like "!!for & bar".

What GCC version btw?

>> When 'bar' is not 0 or 1, it complains with -Werror=parentheses:
>>
>>   suggest parentheses around operand of ‘!’ or change ‘&’ to ‘&&’ or ‘!’ to 
>> ‘~’ [-Werror=parentheses]
>>
>> Add a () around "foo && bar", which also improves code readability.
>>
>> Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
>> ---
>>
>>  hw/dma/sifive_pdma.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/hw/dma/sifive_pdma.c b/hw/dma/sifive_pdma.c
>> index b4fd40573a..b8ec7621f3 100644
>> --- a/hw/dma/sifive_pdma.c
>> +++ b/hw/dma/sifive_pdma.c
>> @@ -243,7 +243,7 @@ static void sifive_pdma_write(void *opaque, hwaddr 
>> offset,
>>      offset &= 0xfff;
>>      switch (offset) {
>>      case DMA_CONTROL:
>> -        claimed = !!s->chan[ch].control & CONTROL_CLAIM;
>> +        claimed = !!(s->chan[ch].control & CONTROL_CLAIM);
> 
> AFAIK in C logical NOT has precedence over bitwise AND, so IIUC
> compilers should read the current code as:
> 
>            claimed (!!s->chan[ch].control) & CONTROL_CLAIM;
> 
> meaning this patch is doing more than "improve code readability",
> this is a logical change and likely a bug fix...
> 
> BTW GCC suggestions are:
> 
>            claimed (!!s->chan[ch].control) & CONTROL_CLAIM;
> 
>            claimed (!!s->chan[ch].control) && CONTROL_CLAIM;
>>  
>>          if (!claimed && (value & CONTROL_CLAIM)) {
>>              /* reset Next* registers */
>>
> 
>