From 33be32d518e17c8f8971fa7c1fe09adcccd82a67 Mon Sep 17 00:00:00 2001
From: "Douglas B. Rumbaugh" <doug@douglasrumbaugh.com>
Date: Sun, 2 Nov 2025 17:57:17 -0500
Subject: Added splitting and some basic testing for it

---
 include/constants.h    |  1 +
 src/free_list.c        | 17 ++++++++++++++++-
 tests/liballoc_tests.c | 30 ++++++++++++++++++++++++++++++
 3 files changed, 47 insertions(+), 1 deletion(-)

diff --git a/include/constants.h b/include/constants.h
index 7d88060..8cb2db7 100644
--- a/include/constants.h
+++ b/include/constants.h
@@ -14,5 +14,6 @@
 
 #define MAGIC_NUMBER 0x123456789
 #define ALIGNMENT 16
+#define SPLIT_THRESHOLD 64
 
 #endif
diff --git a/src/free_list.c b/src/free_list.c
index 11fb59b..6c0ff35 100644
--- a/src/free_list.c
+++ b/src/free_list.c
@@ -22,7 +22,22 @@ free_nd *fl_find_first_fit(free_nd *free_list, size_t size) {
 }
 
 void *fl_split_node(free_nd **free_list, free_nd *split_nd, size_t size) {
-  /* for now, we'll just remove the node from the free list */
+
+  ssize_t extra_space = split_nd->size - size - sizeof(header);
+  if (extra_space >= SPLIT_THRESHOLD) {
+    free_nd *new_nd = (free_nd*)((char*) (split_nd) + size + sizeof(header));
+    new_nd->next = split_nd ->next;
+    split_nd->next = new_nd;
+
+    new_nd->size = extra_space - sizeof(header);
+
+    header *new_hdr = (header *)((char *)new_nd - sizeof(header));
+    new_hdr->magic_number = MAGIC_NUMBER;
+    new_hdr->size = extra_space - sizeof(header);
+
+    header *old_hdr =  (header *)((char *)split_nd- sizeof(header));  
+    old_hdr->size = size;
+  }
 
   if (*free_list == split_nd) {
     *free_list = (*free_list)->next;
diff --git a/tests/liballoc_tests.c b/tests/liballoc_tests.c
index 6e6b537..2d3a439 100644
--- a/tests/liballoc_tests.c
+++ b/tests/liballoc_tests.c
@@ -189,6 +189,34 @@ START_TEST(free_list_coalesce_backward) {
 }
 END_TEST
 
+START_TEST(free_list_split_basic) {
+  size_t initial_size = ALIGNMENT * 10;
+  size_t second_size = ALIGNMENT * 5;
+
+  void *memory = allocate(initial_size);
+  release(memory);
+
+  void *memory2 = allocate(second_size);
+  ck_assert_ptr_eq(memory, memory2);
+
+  ck_assert_ptr_nonnull(free_list_head());
+ 
+}
+END_TEST
+
+START_TEST(free_list_split_below_threshold) {
+  size_t initial_size = 5*ALIGNMENT;
+  size_t second_size = 2*ALIGNMENT;
+
+  void *memory = allocate(initial_size);
+  release(memory);
+
+  void *memory2 = allocate(second_size);
+  ck_assert_ptr_eq(memory, memory2);
+
+  ck_assert_ptr_null(free_list_head());
+}
+
 
 
 Suite *liballoc_suite(void) {
@@ -207,6 +235,8 @@ Suite *liballoc_suite(void) {
   tcase_add_test(unit, free_list_reuse);
   tcase_add_test(unit, free_list_coalesce_forward);
   tcase_add_test(unit, free_list_coalesce_backward);
+  tcase_add_test(unit, free_list_split_basic);
+  tcase_add_test(unit, free_list_split_below_threshold);
 
   suite_add_tcase(s, unit);
   return s;
-- 
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