Re: [PATCH] Do without union of variable length arrays.

[Mark Wielaard <mjw at redhat dot com>]

On 01.10.2015 23:45, Alexander Cherepanov wrote:
>On 2015-09-17 12:40, Mark Wielaard wrote:
>>>* Now const size_t is used instead of const int for malloc argument
>>>type.
>>
>>Thanks. I am still interested in the overflow issue. I believe since we
>>are using unsigned arithmetic and we know the size is always > 0, it
>>should be as simple as doing:
>>
>>   const size_t elem_size = ... sizeof (...);
>>   const size_t bytes = num * elem_size;
>>   if (unlikely (bytes / elem_size != num))
>>     return E_NOMEM;
>>   ... malloc (bytes);
>
>Sorry, I'm late to the party but why not check it before multiplication
>in a usual way:
>
>if (num > SIZE_MAX / elem_size)
>   return E_NOMEM;
>
>IIUC elem_size is a compile time constant so the whole division is
>computed by compiler.

I had not thought of that. Yes, that is a nicer check.

Thanks,

Mark