Re: Popcount optimization using AVX512

Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> writes:
> On 2024-Apr-02, Nathan Bossart wrote:
>> Another idea I had is to turn pg_popcount() into a macro that just uses the
>> pg_number_of_ones array when called for few bytes:
>>
>> static inline uint64
>> pg_popcount_inline(const char *buf, int bytes)
>> {
>> uint64 popcnt = 0;
>>
>> while (bytes--)
>> popcnt += pg_number_of_ones[(unsigned char) *buf++];
>>
>> return popcnt;
>> }
>>
>> #define pg_popcount(buf, bytes) \
>> ((bytes < 64) ? \
>> pg_popcount_inline(buf, bytes) : \
>> pg_popcount_optimized(buf, bytes))
>>
>> But again, I'm not sure this is really worth it for the current use-cases.

> Eh, that seems simple enough, and then you can forget about that case.

I don't like the double evaluation of the macro argument. Seems like
you could get the same results more safely with

static inline uint64
pg_popcount(const char *buf, int bytes)
{
if (bytes < 64)
{
uint64 popcnt = 0;

while (bytes--)
popcnt += pg_number_of_ones[(unsigned char) *buf++];

return popcnt;
}
return pg_popcount_optimized(buf, bytes);
}

regards, tom lane