Handle some predefined read-only number registers, e.g. .H and .V.

In particular, this improves handling of the pod2man(1) preamble;
for examples of the effect, see some author names in perlthrtut(1).

Missing feature reported by Andreas Voegele <mail at andreasvoegele dot com>
more than two years ago.  Written at Christchurch International Airport.

1 files changed, 43 insertions, 0 deletions

diff --git a/roff.c b/roff.c
index 45197765..06ecc9a7 100644
--- a/roff.c
+++ b/roff.c
@@ -192,6 +192,7 @@ static	int		 roff_getnum(const char *, int *, int *);
 static	int		 roff_getop(const char *, int *, char *);
 static	int		 roff_getregn(const struct roff *,
 				const char *, size_t);
+static	int		 roff_getregro(const char *name);
 static	const char	*roff_getstrn(const struct roff *, 
 				const char *, size_t);
 static	enum rofferr	 roff_it(ROFF_ARGS);
@@ -1380,10 +1381,45 @@ roff_setreg(struct roff *r, const char *name, int val, char sign)
 		reg->val = val;
 }
 
+/*
+ * Handle some predefined read-only number registers.
+ * For now, return -1 if the requested register is not predefined;
+ * in case a predefined read-only register having the value -1
+ * were to turn up, another special value would have to be chosen.
+ */
+static int
+roff_getregro(const char *name)
+{
+
+	switch (*name) {
+	case ('A'):  /* ASCII approximation mode is always off. */
+		return(0);
+	case ('g'):  /* Groff compatibility mode is always on. */
+		return(1);
+	case ('H'):  /* Fixed horizontal resolution. */
+		return (24);
+	case ('j'):  /* Always adjust left margin only. */
+		return(0);
+	case ('T'):  /* Some output device is always defined. */
+		return(1);
+	case ('V'):  /* Fixed vertical resolution. */
+		return (40);
+	default:
+		return (-1);
+	}
+}
+
 int
 roff_getreg(const struct roff *r, const char *name)
 {
 	struct roffreg	*reg;
+	int		 val;
+
+	if ('.' == name[0] && '\0' != name[1] && '\0' == name[2]) {
+		val = roff_getregro(name + 1);
+		if (-1 != val)
+			return (val);
+	}
 
 	for (reg = r->regtab; reg; reg = reg->next)
 		if (0 == strcmp(name, reg->key.p))
@@ -1396,6 +1432,13 @@ static int
 roff_getregn(const struct roff *r, const char *name, size_t len)
 {
 	struct roffreg	*reg;
+	int		 val;
+
+	if ('.' == name[0] && 2 == len) {
+		val = roff_getregro(name + 1);
+		if (-1 != val)
+			return (val);
+	}
 
 	for (reg = r->regtab; reg; reg = reg->next)
 		if (len == reg->key.sz &&