Re: Speedup usages of pg_*toa() functions

From: Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk>
To: David Rowley <dgrowleyml(at)gmail(dot)com>
Cc: PostgreSQL Developers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Andres Freund <andres(at)anarazel(dot)de>
Subject: Re: Speedup usages of pg_*toa() functions
Date: 2020-06-09 10:08:34
Message-ID: 87lfkw7eao.fsf@news-spur.riddles.org.uk
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>>>>> "David" == David Rowley <dgrowleyml(at)gmail(dot)com> writes:

David> This allows us to speed up a few cases. int2vectorout() should
David> be faster and int8out() becomes a bit faster if we get rid of
David> the strdup() call and replace it with a palloc()/memcpy() call.

What about removing the memcpy entirely? I don't think we save anything
much useful here by pallocing the exact length, rather than doing what
int4out does and palloc a fixed size and convert the int directly into
it.

i.e.

Datum
int8out(PG_FUNCTION_ARGS)
{
int64 val = PG_GETARG_INT64(0);
char *result = palloc(MAXINT8LEN + 1);

pg_lltoa(val, result);
PG_RETURN_CSTRING(result);
}

For pg_ltoa, etc., I don't like adding the extra call to pg_ultoa_n - at
least on my clang, that results in two copies of pg_ultoa_n inlined.
How about doing it like,

int
pg_lltoa(int64 value, char *a)
{
int len = 0;
uint64 uvalue = value;

if (value < 0)
{
uvalue = (uint64) 0 - uvalue;
a[len++] = '-';
}
len += pg_ulltoa_n(uvalue, a + len);
a[len] = '\0';
return len;
}

--
Andrew (irc:RhodiumToad)

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