The "value" argument to the roff(7) .nr requests ends right before

the first non-digit character.  While here, implement and document
an optional sign, requesting increment or decrement, as documented
in the Ossanna/Kernighan/Ritter troff manual and supported by groff.

Reported by bentley@ on discuss@.

4 files changed, 32 insertions, 16 deletions

diff --git a/libmandoc.h b/libmandoc.h
index 18f200b7..3c005e10 100644
--- a/libmandoc.h
+++ b/libmandoc.h
@@ -1,4 +1,4 @@
-/*	$Id: libmandoc.h,v 1.34 2013/10/05 22:15:03 schwarze Exp $ */
+/*	$Id: libmandoc.h,v 1.35 2013/12/15 21:23:52 schwarze Exp $ */
 /*
  * Copyright (c) 2009, 2010, 2011, 2012 Kristaps Dzonsons <kristaps@bsd.lv>
  * Copyright (c) 2013 Ingo Schwarze <schwarze@openbsd.org>
@@ -68,7 +68,7 @@ void		 roff_reset(struct roff *);
 enum rofferr	 roff_parseln(struct roff *, int, 
 			char **, size_t *, int, int *);
 void		 roff_endparse(struct roff *);
-void		 roff_setreg(struct roff *, const char *, int);
+void		 roff_setreg(struct roff *, const char *, int, char sign);
 int		 roff_getreg(const struct roff *, const char *);
 char		*roff_strdup(const struct roff *, const char *);
 int		 roff_getcontrol(const struct roff *, 
diff --git a/mdoc_validate.c b/mdoc_validate.c
index b8605a83..4cfd6204 100644
--- a/mdoc_validate.c
+++ b/mdoc_validate.c
@@ -1,4 +1,4 @@
-/*	$Id: mdoc_validate.c,v 1.197 2013/10/21 23:47:58 schwarze Exp $ */
+/*	$Id: mdoc_validate.c,v 1.198 2013/12/15 21:23:52 schwarze Exp $ */
 /*
  * Copyright (c) 2008-2012 Kristaps Dzonsons <kristaps@bsd.lv>
  * Copyright (c) 2010, 2011, 2012, 2013 Ingo Schwarze <schwarze@openbsd.org>
@@ -1991,10 +1991,10 @@ post_sh_head(POST_ARGS)
 	/* The SYNOPSIS gets special attention in other areas. */
 
 	if (SEC_SYNOPSIS == sec) {
-		roff_setreg(mdoc->roff, "nS", 1);
+		roff_setreg(mdoc->roff, "nS", 1, '=');
 		mdoc->flags |= MDOC_SYNOPSIS;
 	} else {
-		roff_setreg(mdoc->roff, "nS", 0);
+		roff_setreg(mdoc->roff, "nS", 0, '=');
 		mdoc->flags &= ~MDOC_SYNOPSIS;
 	}
 
diff --git a/roff.7 b/roff.7
index 99e44611..21dd474e 100644
--- a/roff.7
+++ b/roff.7
@@ -1,4 +1,4 @@
-.\"	$Id: roff.7,v 1.44 2013/10/22 20:38:00 schwarze Exp $
+.\"	$Id: roff.7,v 1.45 2013/12/15 21:23:52 schwarze Exp $
 .\"
 .\" Copyright (c) 2010, 2011 Kristaps Dzonsons <kristaps@bsd.lv>
 .\" Copyright (c) 2010, 2011 Ingo Schwarze <schwarze@openbsd.org>
@@ -15,7 +15,7 @@
 .\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 .\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 .\"
-.Dd $Mdocdate: October 22 2013 $
+.Dd $Mdocdate: December 15 2013 $
 .Dt ROFF 7
 .Os
 .Sh NAME
@@ -814,19 +814,22 @@ the name of the request, macro or string to be undefined.
 Currently, it is ignored including its arguments,
 and the number of arguments is not checked.
 .Ss \&nr
-Define a register.
+Define or change a register.
 A register is an arbitrary string value that defines some sort of state,
 which influences parsing and/or formatting.
 Its syntax is as follows:
 .Pp
-.D1 Pf \. Cm \&nr Ar name Ar value
+.D1 Pf \. Cm \&nr Ar name Oo +|- Oc Ns Ar value
 .Pp
 The
 .Ar value
 may, at the moment, only be an integer.
-So far, only the following register
+If it is prefixed by a sign, the register will be 
+incremented or decremented instead of assigned to.
+.Pp
+The following register
 .Ar name
-is recognised:
+is handled specially:
 .Bl -tag -width Ds
 .It Cm nS
 If set to a positive integer value, certain
diff --git a/roff.c b/roff.c
index 83738cef..e4c43c13 100644
--- a/roff.c
+++ b/roff.c
@@ -1,4 +1,4 @@
-/*	$Id: roff.c,v 1.186 2013/10/22 20:38:00 schwarze Exp $ */
+/*	$Id: roff.c,v 1.187 2013/12/15 21:23:52 schwarze Exp $ */
 /*
  * Copyright (c) 2010, 2011, 2012 Kristaps Dzonsons <kristaps@bsd.lv>
  * Copyright (c) 2010, 2011, 2012, 2013 Ingo Schwarze <schwarze@openbsd.org>
@@ -1360,7 +1360,7 @@ roff_ds(ROFF_ARGS)
 }
 
 void
-roff_setreg(struct roff *r, const char *name, int val)
+roff_setreg(struct roff *r, const char *name, int val, char sign)
 {
 	struct roffreg	*reg;
 
@@ -1375,11 +1375,17 @@ roff_setreg(struct roff *r, const char *name, int val)
 		reg = mandoc_malloc(sizeof(struct roffreg));
 		reg->key.p = mandoc_strdup(name);
 		reg->key.sz = strlen(name);
+		reg->val = 0;
 		reg->next = r->regtab;
 		r->regtab = reg;
 	}
 
-	reg->val = val;
+	if ('+' == sign)
+		reg->val += val;
+	else if ('-' == sign)
+		reg->val -= val;
+	else
+		reg->val = val;
 }
 
 int
@@ -1426,14 +1432,21 @@ roff_nr(ROFF_ARGS)
 {
 	const char	*key;
 	char		*val;
+	size_t		 sz;
 	int		 iv;
+	char		 sign;
 
 	val = *bufp + pos;
 	key = roff_getname(r, &val, ln, pos);
 
-	iv = mandoc_strntoi(val, strlen(val), 10);
+	sign = *val;
+	if ('+' == sign || '-' == sign)
+		val++;
+
+	sz = strspn(val, "0123456789");
+	iv = sz ? mandoc_strntoi(val, sz, 10) : 0;
 
-	roff_setreg(r, key, iv);
+	roff_setreg(r, key, iv, sign);
 
 	return(ROFF_IGN);
 }