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

[Markus Armbruster]

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.