1 files changed, 71 insertions, 5 deletions

diff --git a/list.c b/list.c
index ab278a1..d6ecb1a 100644
--- a/list.c
+++ b/list.c
@@ -11,6 +11,9 @@
 #define D(x)
 #endif
 
+/*
+ * Move element in item to the head of list mainlist.
+ */ 
 void movetohead(struct item **mainlist, struct item *item)
 {
     if (NULL == item || NULL == mainlist || NULL == *mainlist)
@@ -20,7 +23,7 @@ void movetohead(struct item **mainlist, struct item *item)
     
     if (*mainlist == item)
     {
-        /* Already at head. Do nothing. */
+        /* item is NULL or we're already at head. Do nothing. */
         return;
     }
 
@@ -35,15 +38,23 @@ void movetohead(struct item **mainlist, struct item *item)
         item->next->prev = item->prev;
     }
 
-    /* Now at head. */
+    /* Now we'at head, so no one before us. */
     item->prev = NULL;
+
+    /* Old head is our next. */
     item->next = *mainlist;
 
+    /* Old head needs to know about us. */
+    item->next->prev = item;
+    
     /* Remember the new head. */
     *mainlist = item;
 }
 
 /*
+ * Create space for a new item and add it to the head of mainlist.
+ *
+ * Returns item or NULL if out of memory.
  */
 struct item *additem(struct item **mainlist)
 {
@@ -120,10 +131,14 @@ void listall(struct item *mainlist)
 {
     struct item *item;
     int i;
+
+    printf("Listing all:\n");
     
     for (item = mainlist, i = 1; item != NULL; item = item->next, i ++)
     {
         printf("%d at %p: %s.\n", i, (void *)item, (char *)item->data);
+        printf("  prev: %p\n", item->prev);
+        printf("  next: %p\n", item->next);
     }
 }
 
@@ -133,7 +148,10 @@ int main(void)
     struct item *item1;
     struct item *item2;
     struct item *item3;
-    struct item *item4;    
+    struct item *item4;
+    struct item *item;
+    struct item *nextitem;
+    int i;
     char *foo1 = "1";
     char *foo2 = "2";
     char *foo3 = "3";
@@ -179,12 +197,58 @@ int main(void)
     printf("Current elements:\n");    
     listall(mainlist);
 
-    movetohead(&mainlist, item2);
+    printf("----------------------------------------------------------------------\n");
+
+    printf("Moving item3 to be after item2\n");
+    movetonext(&mainlist, item2, item3);
+    printf("Current elements:\n");    
+    listall(mainlist);
+
+    printf("----------------------------------------------------------------------\n");
+
+    printf("Moving head! item4 to be after item2\n");
+    movetonext(&mainlist, item2, item4);
     printf("Current elements:\n");    
     listall(mainlist);
+
+    printf("----------------------------------------------------------------------\n");
     
+    printf("Moving tail! item1 to be after item2\n");
+    movetonext(&mainlist, item2, item1);
+    printf("Current elements:\n");
+    listall(mainlist);
+
     printf("----------------------------------------------------------------------\n");
 
+    printf("Moving head to be after tail.\n");
+    movetonext(&mainlist, item3, item2);
+    printf("Current elements:\n");
+    listall(mainlist);
+    
+    printf("Moving all the items after each other.\n");
+    /* item3 is tail. work backwards. */
+    for (item = mainlist, i = 1;
+         item != NULL;
+         item = item->next, i ++)
+    {
+        for (nextitem = item2; nextitem != NULL; nextitem = nextitem->prev)
+        {
+            movetonext(&mainlist, nextitem, item);
+            printf("Current elements:\n");
+            listall(mainlist);
+        }
+    }
+    
+    printf("----------------------------------------------------------------------\n");
+
+#if 0    
+    movetohead(&mainlist, item2);
+    printf("Current elements:\n");    
+    listall(mainlist);
+    
+    printf("----------------------------------------------------------------------\n");
+#endif
+    
     printf("Deleting item stored at %p\n", item3);
     delitem(&mainlist, item3);
     printf("Current elements:\n");    
@@ -203,7 +267,9 @@ int main(void)
     listall(mainlist);
 
     puts("");
-    
+
+    printf("----------------------------------------------------------------------\n");
+               
     exit(0);
 }
 #endif