Re: define pg_structiszero(addr, s, r) - Mailing list pgsql-hackers

On 18/09/2024 21:57, Bertrand Drouvot wrote:
> On Wed, Sep 18, 2024 at 10:03:21AM +0200, Peter Eisentraut wrote:
>> On 18.09.24 06:16, Bertrand Drouvot wrote:
>>> +#define pg_structiszero(addr, s, r)                                    \
>>> +    do {                                                            \
>>> +        /* We assume this initializes to zeroes */                    \
>>> +        static const s all_zeroes;                                    \
>>> +        r = (memcmp(addr, &all_zeroes, sizeof(all_zeroes)) == 0);    \
>>> +    } while (0)

Not new with this patch, but do we guarantee padding bytes to be zeros?

How about this instead:

static inline bool
pg_is_all_zeros(const char *p, size_t len)
{
   for (size_t i = 0; i < len; i++)
   {
     if (p[i] != 0)
         return false;
   }
   return true;
}

Is there's a de facto standard name for that function? I was surprised 
that I couldn't find one with a quick google search. That seems like the 
kind of small utility function that every C program needs.

How performance sensitive is this? If it's not, then the above seems 
like the most straightforward way to do this, which is good. If it is 
performance sensitive, it's still good, because the compiler can 
optimize that well: https://godbolt.org/z/x9hPWjheq.

-- 
Heikki Linnakangas
Neon (https://neon.tech)