From a514490dcbb4aaaca3a5e4fc71ef194fea18b37f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Hugo=20H=C3=B6rnquist?= <hugo@lysator.liu.se>
Date: Tue, 5 Feb 2019 23:17:08 +0100
Subject: Add llist FIRST & LAST, rewrote code to use them.

---
 linked_list.h     |  3 +++
 linked_list.inc.h | 31 ++++++++++++++++++-------------
 scheme.scm.c      |  2 +-
 3 files changed, 22 insertions(+), 14 deletions(-)

diff --git a/linked_list.h b/linked_list.h
index 5bf3db15..515fa4af 100644
--- a/linked_list.h
+++ b/linked_list.h
@@ -22,6 +22,9 @@ typedef struct {
 	int length;
 } LLIST(TYPE);
 
+#define FIRST(lst) (lst)->head->after
+#define LAST(lst)  (lst)->tail->before
+
 INIT_F ( LLIST(TYPE) );
 FREE_F ( LLIST(TYPE) );
 
diff --git a/linked_list.inc.h b/linked_list.inc.h
index 2622eb4b..1522a685 100644
--- a/linked_list.inc.h
+++ b/linked_list.inc.h
@@ -56,10 +56,12 @@ INIT_F ( LINK(TYPE), TYPE* val ) {
 int PUSH(LLIST(TYPE)) ( LLIST(TYPE)* lst, TYPE* val) {
 	NEW(LINK(TYPE), link, val);
 
-	link->after = lst->head->after;
-	lst->head->after = link;
+	link->after         = FIRST(lst);
+	FIRST(lst)          = link;
+
 	link->after->before = link;
-	link->before = lst->head;
+	link->before        = lst->head;
+
 	++lst->length;
 
 	// TODO do I want to change that?
@@ -69,7 +71,7 @@ int PUSH(LLIST(TYPE)) ( LLIST(TYPE)* lst, TYPE* val) {
 }
 
 int DEEP_COPY(LLIST(TYPE)) ( LLIST(TYPE)* dest, LLIST(TYPE)* src ) {
-	LINK(TYPE)* n = src->head->after;
+	LINK(TYPE)* n = FIRST(src);
 
 	while (n->after != NULL) {
 		NEW(TYPE, cpy);
@@ -89,22 +91,25 @@ int DEEP_COPY(LLIST(TYPE)) ( LLIST(TYPE)* dest, LLIST(TYPE)* src ) {
  */
 int APPEND(LLIST(TYPE)) ( LLIST(TYPE)* dest, LLIST(TYPE)* new ) {
 
-	LINK(TYPE)* og_new_head = new->head;
-	dest->tail->before->after = new->head->after;
-	new->head->after->before = dest->tail->before;
-	LINK(TYPE)* old_tail = dest->tail;
+	/* Link end of dest onto start of new. */
+	LAST(dest)->after  = FIRST(new);
+	FIRST(new)->before = LAST(dest);
+
+	/* Free the two now not needed end links.  */
+	free(new->head);
+	free(dest->tail);
+
+	/* Update dest with new tail ptr. */
 	dest->tail = new->tail;
-	dest->length += new->length;
 
-	free(old_tail);
-	free(og_new_head);
+	dest->length += new->length;
 
 	return 0;
 }
 
 int SIZE(LLIST(TYPE)) ( LLIST(TYPE)* llist ) {
 	int size = 0;
-	LINK(TYPE)* l = llist->head->after;
+	LINK(TYPE)* l = FIRST(llist);
 	while (l->after != NULL) {
 		++size;
 	}
@@ -112,7 +117,7 @@ int SIZE(LLIST(TYPE)) ( LLIST(TYPE)* llist ) {
 }
 
 int EMPTY(LLIST(TYPE)) ( LLIST(TYPE)* llist ) {
-	return llist->head->after == llist->tail;
+	return FIRST(llist) == llist->tail;
 }
 
 #endif /* TYPE */
diff --git a/scheme.scm.c b/scheme.scm.c
index da8cd3f1..a7ddc27d 100644
--- a/scheme.scm.c
+++ b/scheme.scm.c
@@ -53,7 +53,7 @@ SCM_DEFINE (calendar_get_attr, "calendar-get-attr", 3, 0, 0,
 
 	// TODO actuall iterators
 	// TODO this reverses the list
-	for ( LINK(strbuf)* n = c->vals.head->after;
+	for ( LINK(strbuf)* n = FIRST(&c->vals);
 			n->after != NULL;
 			n = n->after) {
 		llist = scm_cons(scm_from_strbuf(n->value), llist);
-- 
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