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

[Bin Meng]

Hi Markus,

On Mon, Sep 27, 2021 at 2:51 PM Markus Armbruster <armbru@redhat.com> wrote:
>
> Bin Meng <bmeng.cn@gmail.com> writes:
>
> > GCC seems to be strict about processing pattern like "!!for & bar".
> > 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);
> >
> >          if (!claimed && (value & CONTROL_CLAIM)) {
> >              /* reset Next* registers */
>
> Old code
>
>     first double-negate, mapping zero to zero, non-zero to one
>     then mask, which does nothing, because CONTROL_CLAIM is 1
>
> New code:
>
>     first mask, yielding 0 or 1
>     then double-negate, which does nothing
>
> Looks like a bug fix to me.  If I'm right, the commit message is wrong,
> and the double negate is redundant.
>

Thanks for the review. The double negate is not needed with
CONTROL_CLAIM which is 1, but is needed if the bit is in another
position.

Regards,
Bin