mdocml: Add support for EQNPOS_SUBSUP and a doubly-linked eqn_box list.

[kristaps@mdocml.bsd.lv]

Log Message:
-----------
Add support for EQNPOS_SUBSUP and a doubly-linked eqn_box list.

Modified Files:
--------------
    mdocml:
        mandoc.h
        eqn.c

Revision Data
-------------
Index: eqn.c
===================================================================
RCS file: /usr/vhosts/mdocml.bsd.lv/cvs/mdocml/eqn.c,v
retrieving revision 1.45
retrieving revision 1.46
diff -Leqn.c -Leqn.c -u -p -r1.45 -r1.46
--- eqn.c
+++ eqn.c
@@ -198,6 +198,7 @@ static	const struct eqnstr eqnposs[EQNPO
 	{ "", 0 }, /* EQNPOS_NONE */
 	{ "over", 4 }, /* EQNPOS_OVER */
 	{ "sup", 3 }, /* EQNPOS_SUP */
+	{ NULL, 0 }, /* EQNPOS_SUPSUB */
 	{ "sub", 3 }, /* EQNPOS_SUB */
 	{ "to", 2 }, /* EQNPOS_TO */
 	{ "from", 4 }, /* EQNPOS_FROM */
@@ -569,14 +570,30 @@ eqn_box(struct eqn_node *ep, struct eqn_
 		return(EQN_OK);
 	}
 
+	/*
+	 * Positional elements (e.g., over, sub, sup, ...).
+	 */
 	for (i = 0; i < (int)EQNPOS__MAX; i++) {
-		if ( ! EQNSTREQ(&eqnposs[i], start, sz))
+		/* Some elements don't have names (are virtual). */
+		if (NULL == eqnposs[i].name)
+			continue;
+		else if ( ! EQNSTREQ(&eqnposs[i], start, sz))
 			continue;
 		if (NULL == last->last) {
 			EQN_MSG(MANDOCERR_EQNSYNT, ep);
 			return(EQN_ERR);
 		}
-		last->last->pos = (enum eqn_post)i;
+		/*
+		 * If we encounter x sub y sup z, then according to the
+		 * eqn manual, we regard this as x subsup y z.
+		 */
+		if (EQNPOS_SUP == i &&
+			NULL != last->last->prev &&
+			EQNPOS_SUB == last->last->prev->pos)
+			last->last->prev->pos = EQNPOS_SUBSUP;
+		else
+			last->last->pos = (enum eqn_post)i;
+
 		if (EQN_EOF == (c = eqn_box(ep, last))) {
 			EQN_MSG(MANDOCERR_EQNEOF, ep);
 			return(EQN_ERR);
@@ -665,10 +682,11 @@ eqn_box_alloc(struct eqn_node *ep, struc
 	bp->parent = parent;
 	bp->size = ep->gsize;
 
-	if (NULL == parent->first)
-		parent->first = bp;
-	else
+	if (NULL != parent->first) {
 		parent->last->next = bp;
+		bp->prev = parent->last;
+	} else
+		parent->first = bp;
 
 	parent->last = bp;
 	return(bp);
Index: mandoc.h
===================================================================
RCS file: /usr/vhosts/mdocml.bsd.lv/cvs/mdocml/mandoc.h,v
retrieving revision 1.156
retrieving revision 1.157
diff -Lmandoc.h -Lmandoc.h -u -p -r1.156 -r1.157
--- mandoc.h
+++ mandoc.h
@@ -336,6 +336,7 @@ enum	eqn_post {
 	EQNPOS_NONE = 0,
 	EQNPOS_OVER,
 	EQNPOS_SUP,
+	EQNPOS_SUBSUP,
 	EQNPOS_SUB,
 	EQNPOS_TO,
 	EQNPOS_FROM,
@@ -366,6 +367,7 @@ struct	eqn_box {
 	struct eqn_box	 *first; /* first child node */
 	struct eqn_box	 *last; /* last child node */
 	struct eqn_box	 *next; /* node sibling */
+	struct eqn_box	 *prev; /* node sibling */
 	struct eqn_box	 *parent; /* node sibling */
 	char		 *text; /* text (or NULL) */
 	char		 *left;
--
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