Horton

Re: Performance improvements for src/port/snprintf.c

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
Cc: Alexander Kuzmenkov <a.kuzmenkov@postgrespro.ru>, pgsql-hackers@lists.postgresql.org
Date: 2018-10-02T22:04:33Z
Lists: pgsql-hackers 
Andres Freund <andres@anarazel.de> writes:
> I've looked through the patch. Looks good to me. Some minor notes:

[ didn't see this till after sending my previous ]

> - How about adding our own strchrnul for the case where we don't
>   HAVE_STRCHRNUL?  It's possible that other platforms have something
>   similar, and the code wouldlook more readable that way.

Sure, we could just make a "static inline strchrnul()" for use when
!HAVE_STRCHRNUL.  No objection.

> - I know it's not new, but is it actually correct to use va_arg(args, int64)
>   for ATYPE_LONGLONG?

Well, the problem with just doing s/int64/long long/g is that the
code would then fail on compilers without a "long long" type.
We could ifdef our way around that, but I don't think the code would
end up prettier.

Given that we only ever use "ll" modifiers via INT64_FORMAT, and that
that'll only be set to "ll" if int64 is indeed "long long", those code
paths should be dead code in any situation where the type pun is wrong.

			regards, tom lane

Commits

  1. Improve snprintf.c's handling of NaN, Infinity, and minus zero.

  2. Rationalize snprintf.c's handling of "ll" formats.

  3. Provide fast path in snprintf.c for conversion specs that are just "%s".

  4. Make assorted performance improvements in snprintf.c.

  5. Set snprintf.c's maximum number of NL arguments to be 31.

  6. Always use our own versions of *printf().