Make assorted performance improvements in snprintf.c.

tglsfdc · tglsfdc · commit abd9ca377d66 · 2018-10-03T10:18:15.000-04:00
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
diff --git a/configure b/configure
@@ -15100,7 +15100,7 @@ fi
 LIBS_including_readline="$LIBS"
 LIBS=`echo "$LIBS" | sed -e 's/-ledit//g' -e 's/-lreadline//g'`
 
-for ac_func in cbrt clock_gettime fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll posix_fallocate ppoll pstat pthread_is_threaded_np readlink setproctitle setproctitle_fast setsid shm_open symlink sync_file_range utime utimes wcstombs_l
+for ac_func in cbrt clock_gettime fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll posix_fallocate ppoll pstat pthread_is_threaded_np readlink setproctitle setproctitle_fast setsid shm_open strchrnul symlink sync_file_range utime utimes wcstombs_l
 do :
   as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
 ac_fn_c_check_func "$LINENO" "$ac_func" "$as_ac_var"
diff --git a/configure.in b/configure.in
@@ -1571,7 +1571,7 @@ PGAC_FUNC_WCSTOMBS_L
 LIBS_including_readline="$LIBS"
 LIBS=`echo "$LIBS" | sed -e 's/-ledit//g' -e 's/-lreadline//g'`
 
-AC_CHECK_FUNCS([cbrt clock_gettime fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll posix_fallocate ppoll pstat pthread_is_threaded_np readlink setproctitle setproctitle_fast setsid shm_open symlink sync_file_range utime utimes wcstombs_l])
+AC_CHECK_FUNCS([cbrt clock_gettime fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll posix_fallocate ppoll pstat pthread_is_threaded_np readlink setproctitle setproctitle_fast setsid shm_open strchrnul symlink sync_file_range utime utimes wcstombs_l])
 
 AC_REPLACE_FUNCS(fseeko)
 case $host_os in
diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in
@@ -523,6 +523,9 @@
 /* Define to 1 if you have the <stdlib.h> header file. */
 #undef HAVE_STDLIB_H
 
+/* Define to 1 if you have the `strchrnul' function. */
+#undef HAVE_STRCHRNUL
+
 /* Define to 1 if you have the `strerror_r' function. */
 #undef HAVE_STRERROR_R
 
diff --git a/src/include/pg_config.h.win32 b/src/include/pg_config.h.win32
@@ -394,6 +394,9 @@
 /* Define to 1 if you have the <stdlib.h> header file. */
 #define HAVE_STDLIB_H 1
 
+/* Define to 1 if you have the `strchrnul' function. */
+/* #undef HAVE_STRCHRNUL */
+
 /* Define to 1 if you have the `strerror_r' function. */
 /* #undef HAVE_STRERROR_R */
 
diff --git a/src/port/snprintf.c b/src/port/snprintf.c
