3 files changed, 37 insertions, 14 deletions

diff --git a/doc.c b/doc.c
index d5da6bf..3d1b378 100644
--- a/doc.c
+++ b/doc.c
@@ -5,6 +5,8 @@
 #include "doc.h"
 #include "err.h"
 
+/* initialization / destruction */
+
 void doc_init(struct doc *d) {
 	buf_init(&d->txt, sizeof(struct doc_line));
 	buf_init(&d->lnk, 1);
@@ -22,6 +24,8 @@ void doc_fini(struct doc *d) {
 	buf_free(&d->lnk);
 }
 
+/* line creation */
+
 void doc_new_line(struct doc *d) {
 	buf_grow(&d->txt, sizeof(struct doc_line));
 	*(struct doc_line *)&d->txt.buf[d->txt.sz] = (struct doc_line) {
@@ -49,3 +53,29 @@ void doc_add_textn(struct doc *d, const char *s, size_t n) {
 	d->txt.sz += n;
 	dl->len += n;
 }
+
+/* line navigation */
+
+struct doc_line *doc_line_at(struct doc *d, size_t ofs) {
+	return (struct doc_line *)&d->txt.buf[ofs];
+}
+
+int doc_line_prev(struct doc *d, size_t *ofs) {
+	size_t n = doc_line_at(d, *ofs)->prev + sizeof(struct doc_line);
+	if (*ofs >= n) {
+		*ofs -= n;
+		return 0;
+	} else {
+		return -1;
+	}
+}
+
+int doc_line_next(struct doc *d, size_t *ofs) {
+	size_t n = doc_line_at(d, *ofs)->len + sizeof(struct doc_line);
+	if (*ofs + n < d->txt.sz) {
+		*ofs += n;
+		return 0;
+	} else {
+		return -1;
+	}
+}
diff --git a/doc.h b/doc.h
index 496b631..972134b 100644
--- a/doc.h
+++ b/doc.h
@@ -30,4 +30,8 @@ void doc_add_line(struct doc *, const char *);
 void doc_add_text(struct doc *, const char *);
 void doc_add_textn(struct doc *, const char *, size_t);
 
+struct doc_line *doc_line_at(struct doc *d, size_t ofs);
+int doc_line_prev(struct doc *d, size_t *ofs);
+int doc_line_next(struct doc *d, size_t *ofs);
+
 #endif
diff --git a/nav.c b/nav.c
index 8df829e..6d81ddd 100644
--- a/nav.c
+++ b/nav.c
@@ -51,26 +51,15 @@ size_t pg_lines(void) {
 }
 
 struct doc_line *nav_cur_line(struct nav_state *ns) {
-	return (struct doc_line *)&ns->histv[ns->cur_doc].txt.buf[ns->cur_ofs[ns->cur_doc]];
+	return doc_line_at(&ns->histv[ns->cur_doc], ns->cur_ofs[ns->cur_doc]);
 }
 
 int nav_line_up(struct nav_state *ns) {
-	if (ns->cur_ofs[ns->cur_doc] > 0) {
-		ns->cur_ofs[ns->cur_doc] -= nav_cur_line(ns)->prev + sizeof(struct doc_line); 
-		return 1;
-	} else {
-		return 0;
-	}
+	return !doc_line_prev(&ns->histv[ns->cur_doc], &ns->cur_ofs[ns->cur_doc]);
 }
 
 int nav_line_down(struct nav_state *ns) {
-	struct doc_line *l = nav_cur_line(ns);
-	if (ns->cur_ofs[ns->cur_doc] + sizeof(struct doc_line) + l->len < ns->histv[ns->cur_doc].txt.sz) {
-		ns->cur_ofs[ns->cur_doc] += l->len + sizeof(struct doc_line); 
-		return 1;
-	} else {
-		return 0;
-	}
+	return !doc_line_next(&ns->histv[ns->cur_doc], &ns->cur_ofs[ns->cur_doc]);
 }
 
 void nav_pg_up(struct nav_state *ns) {