[dm-devel] [PATCH 5/6] vector: add lower boundary check in vector_foreach_slot_after

[Zhiqiang Liu]

On 2020/8/17 17:11, Martin Wilck wrote:
> On Sun, 2020-08-16 at 09:45 +0800, Zhiqiang Liu wrote:
>> In vector_foreach_slot_after macro, i is the input var, which
>> may have a illegal value (i < 0). So we should add lower boundary
>> check in vector_foreach_slot_after macro.
>>
>> Signed-off-by: Zhiqiang Liu <liuzhiqiang26 at huawei.com>
>> Signed-off-by: lixiaokeng <lixiaokeng at huawei.com>
>> ---
>>  libmultipath/vector.h | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> Perhaps we should write this instead? I'm unsure if compilers can
> optimize away the repeated extra check in all cases.
> 
> #define vector_foreach_slot_after(v,p,i) \
> 	if ((v) && (int)(i) >= 0)        \
> 		for (; (int)(i) < VECTOR_SIZE(v) && ((p) = (v)->slot[i]); (i)++)
> 
> Regards,
> Martin
> 
Thanks for your advice.
When I modified the vector_foreach_slot_after func, I just focused
on the basic functionality, and the performance is totally not considered.
I learn a lesson from your advice.

Thanks again.

Regards
Zhiqiang Liu

>>
>> diff --git a/libmultipath/vector.h b/libmultipath/vector.h
>> index 2862dc2..45dbfc1 100644
>> --- a/libmultipath/vector.h
>> +++ b/libmultipath/vector.h
>> @@ -38,11 +38,11 @@ typedef struct _vector *vector;
>>  #define VECTOR_LAST_SLOT(V)   (((V) && VECTOR_SIZE(V) > 0) ? (V)-
>>> slot[(VECTOR_SIZE(V) - 1)] : NULL)
>>
>>  #define vector_foreach_slot(v,p,i) \
>> -	for (i = 0; (v) && (int)i < VECTOR_SIZE(v) && ((p) = (v)-
>>> slot[i]); i++)
>> +	for ((i) = 0; (v) && (int)(i) < VECTOR_SIZE(v) && ((p) = (v)-
>>> slot[i]); (i)++)
>>  #define vector_foreach_slot_after(v,p,i) \
>> -	for (; (v) && (int)i < VECTOR_SIZE(v) && ((p) = (v)->slot[i]);
>> i++)
>> +	for (; (v) && (int)(i) < VECTOR_SIZE(v) && (int)(i) >= 0 &&
>> ((p) = (v)->slot[i]); (i)++)
>>  #define vector_foreach_slot_backwards(v,p,i) \
>> -	for (i = VECTOR_SIZE(v) - 1; (int)i >= 0 && ((p) = (v)-
>>> slot[i]); i--)
>> +	for ((i) = VECTOR_SIZE(v) - 1; (int)(i) >= 0 && ((p) = (v)-
>>> slot[i]); (i)--)
>>
>>  #define identity(x) (x)
>>  /*
> 
> 
> 
> .
>