[dpdk-dev] [PATCH v3 11/24] rte_mbuf.h: avoid warnings from inadvertant promotion

[Andy Green]

On 05/14/2018 12:54 AM, Thomas Monjalon wrote:
> 12/05/2018 03:59, Andy Green:
>> @@ -836,8 +836,9 @@ rte_mbuf_refcnt_update(struct rte_mbuf *m, int16_t value)
>>   	 * reference counter can occur.
>>   	 */
>>   	if (likely(rte_mbuf_refcnt_read(m) == 1)) {
>> -		rte_mbuf_refcnt_set(m, 1 + value);
>> -		return 1 + value;
>> +		++value;
>> +		rte_mbuf_refcnt_set(m, value);
>> +		return value;
>>   	}
> 
> I don't understand what it is fixing.
> Please could you explain or show the GCC warning?

"1 + value", where value is an uint16_t causes promotion to a signed 
int.  The compiler complained that we are shoving an int into a uint16_t 
return type with different size and sign.

Bumping and returning value directly instead removes the promotion and 
the problem.

I added this explanation to the patch (although the title gave a big 
clue already).

-Andy

>