Make assorted performance improvements in snprintf.c.
In combination, these changes make our version of snprintf as fast
or faster than most platforms' native snprintf, except for cases
involving floating-point conversion (which we still delegate to
the native sprintf). The speed penalty for a float conversion
is down to around 10% though, much better than before.
Notable changes:
* Rather than always parsing the format twice to see if it contains
instances of %n$, do the extra scan only if we actually find a $.
This obviously wins for non-localized formats, and even when there
is use of %n$, we can avoid scanning text before the first % twice.
* Use strchrnul() if available to find the next %, and emit the
literal text between % escapes as strings rather than char-by-char.
* Create a bespoke function (dopr_outchmulti) for the common case
of emitting N copies of the same character, in place of writing
loops around dopr_outch.
* Simplify construction of the format string for invocations of sprintf
for floats.
* Const-ify some internal functions, and avoid unnecessary use of
pass-by-reference arguments.
Patch by me, reviewed by Andres Freund
Discussion: https://postgr.es/m/11787.1534530779@sss.pgh.pa.us
Branch
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master
Details
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https://git.postgresql.org/pg/commitdiff/abd9ca377d669a6e0560e854d7e987438d0e612e
Modified Files
--------------
configure | 2 +-
configure.in | 2 +-
src/include/pg_config.h.in | 3 +
src/include/pg_config.h.win32 | 3 +
src/port/snprintf.c | 695 ++++++++++++++++++++++++++----------------
5 files changed, 432 insertions(+), 273 deletions(-)