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Re: [PATCH 1/2] hw/dma: sifive_pdma: Improve code readability for "!!foo
From: |
Philippe Mathieu-Daudé |
Subject: |
Re: [PATCH 1/2] hw/dma: sifive_pdma: Improve code readability for "!!foo & bar" |
Date: |
Mon, 27 Sep 2021 07:18:00 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.1.0 |
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 */
>>
>
>