Re: [patch] bit XOR aggregate functions

At Tue, 9 Feb 2021 15:25:19 +0000, Alexey Bashtanov <bashtanov@imap.cc> wrote in 
> I personally use it as a checksum for a large unordered set, where
> performance and simplicity is prioritized over collision resilience.
> Maybe there are other ways to use them.

FWIW the BIT_XOR can be created using CREATE AGGREGATE.

CREATE OR REPLACE AGGREGATE BIT_XOR(IN v smallint) (SFUNC = int2xor, STYPE = smallint);
CREATE OR REPLACE AGGREGATE BIT_XOR(IN v int4) (SFUNC = int4xor, STYPE = int4);
CREATE OR REPLACE AGGREGATE BIT_XOR(IN v bigint) (SFUNC = int8xor, STYPE = bigint);
CREATE OR REPLACE AGGREGATE BIT_XOR(IN v bit) (SFUNC = bitxor, STYPE = bit);

The bit_and/bit_or aggregates are back to 2004, that commit says that:

> commit 8096fe45cee42ce02e602cbea08e969139a77455
> Author: Bruce Momjian <bruce@momjian.us>
> Date:   Wed May 26 15:26:28 2004 +0000
...
>    (2) bitwise integer aggregates named bit_and and bit_or for
>        int2, int4, int8 and bit types. They are not standard, but I find
>        them useful. I needed them once.

We already had CREATE AGGREATE at the time, so BIT_XOR can be thought
as it falls into the same category with BIT_AND and BIT_OR, that is,
we may have BIT_XOR as an intrinsic aggregation?

regards.

-- 
Kyotaro Horiguchi
NTT Open Source Software Center