Fixed a major bug involving and pointers

main.c

@@ -68,8 +68,9 @@ int validate_record(struct AllocationRecord *record) {
 }
 
 void new_region(struct AllocationRecord *dummy, struct Arena *arena) {
-  int size = 1 + (rand() % 8192);
-  int align = 1 << (rand() % 4);
+  uintptr_t size = 1 + (rand() % 8192);
+  uintptr_t align = 1 << (rand() % 4);
+  printf("alloc'ing a region of size %lu with alignment %lu, id %i\n", size, align, dummy->id);
   void *region = alloc(arena, size, align);
   if (region == NULL) {
     printf("memory allocator broke, we have 1L though\n");
@@ -87,6 +88,7 @@ void delete_region(struct AllocationRecord *dummy, struct Arena *arena) {
   }
   uintptr_t which = rand() % dummy->size;
   struct AllocationRecord *zap = get_record(dummy, which);
+  printf("dealloc'ing a region of size %lu, id %i\n", zap->size, zap->id);
   unalloc(arena, zap->allocation);
   delete_record(dummy, zap);
 }

tree_alloc.c

@@ -80,6 +80,34 @@ TreeAlloc *search_by_size(TreeAlloc *root, uintptr_t padding, uintptr_t align, u
   }
 }
 
+TreeAlloc *succ(TreeAlloc *el) {
+  if (el->right != NULL) {
+    el = el->right;
+    while (el->left != NULL) {
+      el = el->left;
+    }
+    return el;
+  }
+  while (el->parent != NULL && el == el->parent->right) {
+    el = el->parent;
+  }
+  return el->parent;
+}
+
+TreeAlloc *pred(TreeAlloc *el) {
+  if (el->left != NULL) {
+    el = el->left;
+    while (el->right != NULL) {
+      el = el->right;
+    }
+    return el;
+  }
+  while (el->parent != NULL && el == el->parent->left) {
+    el = el->parent;
+  }
+  return el->parent;
+}
+
 TreeAlloc *get_sibling(TreeAlloc *ta) {
 	TreeAlloc *p = ta->parent;
 	if (!p)
@@ -437,6 +465,19 @@ void *alloc(Arena *arena, uintptr_t size, uintptr_t align) {
         FreeSpace *insert_point = (FreeSpace*) search_by_size((TreeAlloc*) arena->root_freespace, 0, 1, new_free_size);
         insert_left((TreeAlloc**) &arena->root_freespace, (TreeAlloc*) new_free, (TreeAlloc*) insert_point);
       }
+      // Set the region following this one to be the new free space
+      region->after = (TreeAlloc*) new_free;
+    } else {
+      // There isn't a free space after this one, so put the `next` pointer at the next allocated
+      // region.
+      region->after = succ(region);
+    }
+    // Also make sure the `before` pointer is correct.
+    TreeAlloc *before_alloc = pred(region);
+    if (before_alloc == NULL || ((void*) before_alloc) + before_alloc->size < (void*) region) {
+      region->before = search_by_address((TreeAlloc*) arena->root_freespace, region);
+    } else {
+      region->before = before_alloc;
     }
     return align_after(region + sizeof(TreeAlloc), actual_align);
   }