Add buddy_arena_free_size

buddy_alloc.h

@@ -56,6 +56,10 @@ unsigned int buddy_is_full(struct buddy *buddy);
 /* Reports the arena size */
 size_t buddy_arena_size(struct buddy *buddy);
 
+/* Reports the arena's free size. Note that this is (often) not a continuous size
+   but the sum of all free slots in the buddy. */
+size_t buddy_arena_free_size(struct buddy *buddy);
+
 /*
  * Allocation functions
  */
@@ -547,6 +551,26 @@ size_t buddy_arena_size(struct buddy *buddy) {
     return buddy->memory_size;
 }
 
+size_t buddy_arena_free_size(struct buddy *buddy) {
+    size_t result = 0;
+    struct buddy_tree *tree = buddy_tree(buddy);
+    size_t tree_order = buddy_tree_order(tree);
+
+    struct buddy_tree_walk_state state = buddy_tree_walk_state_root();
+    do {
+        size_t pos_status = buddy_tree_status(tree, state.current_pos);
+        if (pos_status == (tree_order - state.current_pos.depth + 1)) { // Fully-allocated
+            state.going_up = 1;
+        } else if (pos_status == 0) { // Free
+            state.going_up = 1;
+            result += size_for_depth(buddy, state.current_pos.depth);
+        } else { // Partial
+            continue;
+        }
+    } while (buddy_tree_walk(tree, &state));
+    return result;
+}
+
 static size_t buddy_tree_order_for_memory(size_t memory_size) {
     size_t blocks = memory_size / BUDDY_ALLOC_ALIGN;
     return highest_bit_position(ceiling_power_of_two(blocks));

tests.c

@@ -576,6 +576,43 @@ void test_buddy_arena_size() {
 	assert(buddy_arena_size(buddy) == 4096);
 }
 
+void test_buddy_arena_free_size_01() {
+	start_test;
+	unsigned char *buddy_buf = malloc(buddy_sizeof(4096));
+	unsigned char data_buf[4096];
+	struct buddy *buddy = buddy_init(buddy_buf, data_buf, 4096);
+	assert(buddy_arena_free_size(buddy) == 4096);
+	void *slot = buddy_malloc(buddy, 4096);
+	assert(buddy_arena_free_size(buddy) == 0);
+	buddy_free(buddy, slot);
+	assert(buddy_arena_free_size(buddy) == 4096);
+	free(buddy_buf);
+}
+
+void test_buddy_arena_free_size_02() {
+	start_test;
+	unsigned char *buddy_buf = malloc(buddy_sizeof(4096));
+	unsigned char data_buf[4096];
+	struct buddy *buddy = buddy_init(buddy_buf, data_buf, 3072);
+	assert(buddy_arena_free_size(buddy) == 3072);
+	void *slot = buddy_malloc(buddy, 2048);
+	assert(buddy_arena_free_size(buddy) == 1024);
+	buddy_free(buddy, slot);
+	assert(buddy_arena_free_size(buddy) == 3072);
+	free(buddy_buf);
+}
+
+void test_buddy_arena_free_size_03() {
+	start_test;
+	unsigned char shared_buf[8192];
+	struct buddy *buddy = buddy_embed(shared_buf, 8192);
+	size_t current_free = buddy_arena_free_size(buddy);
+	void *slot = buddy_malloc(buddy, 2048);
+	assert(buddy_arena_free_size(buddy) == current_free - 2048);
+	buddy_free(buddy, slot);
+	assert(buddy_arena_free_size(buddy) == current_free);
+}
+
 void test_buddy_malloc_null() {
 	start_test;
 	assert(buddy_malloc(NULL, 1024) == NULL);
@@ -2061,6 +2098,9 @@ int main() {
 
 		test_buddy_can_shrink();
 		test_buddy_arena_size();
+		test_buddy_arena_free_size_01();
+		test_buddy_arena_free_size_02();
+		test_buddy_arena_free_size_03();
 
 		test_buddy_malloc_null();
 		test_buddy_malloc_zero();