Re: popcount

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От Daniel Verite
Тема Re: popcount
Дата
Msg-id 5ea2932e-50f5-4a74-9550-5e3291b6652b@manitou-mail.org
обсуждение исходный текст
Ответ на popcount  (David Fetter <david@fetter.org>)
Ответы Re: popcount  (David Fetter <david@fetter.org>)
Список pgsql-hackers
    David Fetter wrote:

+Datum
+byteapopcount(PG_FUNCTION_ARGS)
+{
+    bytea    *t1 = PG_GETARG_BYTEA_PP(0);
+    int        len, result;
+
+    len = VARSIZE_ANY_EXHDR(t1);
+    result = pg_popcount(VARDATA_ANY(t1), len);
+
+    PG_RETURN_INT32(result);
+}

The input may have more than 2 billion bits set to 1. The biggest possible
result should be 8 billion for bytea (1 GB with all bits set to 1).
So shouldn't this function return an int8?

There is a pre-existing function in core: bit_length(bytea) returning int4,
but it errors out for large values (in fact it's a SQL function that returns
octet_length($1)*8).

For the varbit case, it doesn't seem like it can hold so many bits, although
I don't see the limit documented in
https://www.postgresql.org/docs/current/datatype-bit.html


Best regards,
--
Daniel Vérité
PostgreSQL-powered mailer: https://www.manitou-mail.org
Twitter: @DanielVerite



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