Re: roff.c question

[Ingo Schwarze <schwarze@usta.de>]

Hi,

> i'm tempted to do some measurements...

I took the ksh(1) manual, which is rather large,
but a real-word manual with few user-defined strings,
concatenated it 20 times to iteslf (only one header,
of course), and added one .ds near the beginning,
such that roff_res() gets called.  The result is a bit
above 100k lines, two and a half MB total size.

Timing for mandoc -Tlint -Wfatal test.1 on my notebook is:

  three checks up front:  1.40s
  delayed checks:         1.39s
  with strchr:            1.39s

  calling roff_res N times instead of once:
  N=0:                    1.37s
  N=100, strchr:          3.25s
  N=100, up front:        4.45s

So, time spent in roff_res() is about 2.2 percent of
the total parsing time, and we can save nearly 40 percent
of these 2.2 percent.

Thus, on a typical mdoc(7) manual, we economize
between 0.8 and 0.9 percent parsing time with these
optimizations.  Rendering time is about 0.55s,
so we save about 0.6 percent total time.

Given that the rendering time for the ksh(1) manual
is 100 milliseconds on my notebook, we can save
600 microseconds in absolute numbers, on a large
manual.

Thus, here is a version using these optimizations, which
fortunately does not make the code more complicated.
I diffed against OpenBSD, because that makes the
diff easier to understand.

Yours,
  Ingo


Index: roff.c
===================================================================
RCS file: /cvs/src/usr.bin/mandoc/roff.c,v
retrieving revision 1.23
diff -u -p -r1.23 roff.c
--- roff.c	9 Dec 2010 20:56:30 -0000	1.23
+++ roff.c	10 Dec 2010 22:58:19 -0000
@@ -345,18 +345,11 @@ roff_res(struct roff *r, char **bufp, si
 	size_t		 nsz;
 	char		*n;
 
-	/* String escape sequences have at least three characters. */
+	/* Search for a leading backslash and save a pointer to it. */
 
-	for (cp = *bufp + pos; cp[0] && cp[1] && cp[2]; cp++) {
-
-		/*
-		 * The first character must be a backslash.
-		 * Save a pointer to it.
-		 */
-
-		if ('\\' != *cp)
-			continue;
-		stesc = cp;
+	cp = *bufp + pos;
+	while (NULL != (cp = strchr(cp, '\\'))) {
+		stesc = cp++;
 
 		/*
 		 * The second character must be an asterisk.
@@ -364,7 +357,9 @@ roff_res(struct roff *r, char **bufp, si
 		 * so it can't start another escape sequence.
 		 */
 
-		if ('*' != *(++cp))
+		if ('\0' == *cp)
+			return(1);
+		if ('*' != *cp++)
 			continue;
 
 		/*
@@ -373,7 +368,9 @@ roff_res(struct roff *r, char **bufp, si
 		 * Save a pointer to the name.
 		 */
 
-		switch (*(++cp)) {
+		switch (*cp) {
+		case ('\0'):
+			return(1);
 		case ('('):
 			cp++;
 			maxl = 2;
--
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