some small progress on the borrow allocator

allocator.h

@@ -10,6 +10,9 @@ typedef union any_align { char c; int i; long l; long long ll; float f; double d
 #define KB (1024)
 #define MB (KB * KB)
 #define GB (KB * KB * KB)
+#define OFFSET(STRUCT, FIELD) ((size_t) (&((STRUCT*) NULL)->FIELD))
+#define PTR_FROM_FIELD_PTR(STRUCT, FIELD, PTR) ((STRUCT *) (((char *) PTR) - OFFSET(STRUCT, FIELD)))
+
 
 // Contains all operations an allocator can do. Similar interface to sdtlibs
 // malloc, realloc and free.

borrow_allocator.c

@@ -1,17 +1,25 @@
 #include "allocator.h"
 
-
 void *borrow_allcoator_alloc(borrow_allocator_t *this, size_t bytes) {
     linked_allocation_node_t *node = malloc(sizeof(*this->head) + bytes);
+    if (node == NULL) { return NULL; }
     node->prev = NULL;
     node->next = this->head;
     if (this->head != NULL) {
-        // TODO: correct?
+        this->head->prev = node;
-        this->head.prev = node;
     }
     this->head = node;
 }
+
+// WARNING: it is important to consider the case where the old_node is the head
+// node.
+
 void *borrow_allcoator_resize(borrow_allocator_t *this, void *old_ptr, size_t bytes) {
+    linked_allocation_node_t *old_node = PTR_FROM_FIELD_PTR(linked_allocation_node_t, data, old_ptr);
+    // TODO: update the links
 }
 void borrow_allcoator_free(borrow_allocator_t *this, void *old_ptr) {
+    linked_allocation_node_t *old_node = PTR_FROM_FIELD_PTR(linked_allocation_node_t, data, old_ptr);
+    // TODO: update the links
+    free(old_node);
 }