Fix first fit implementation of heap

heap/src/lib.rs

@@ -61,7 +61,7 @@ impl Heap {
     unsafe fn find_first_fit(&self, size: usize) -> Result<*mut HeapHeader, NovaError> {
         let mut current = self.start_address;
         while !fits(size, current) {
-            if let Some(next) = (*self.start_address).next {
+            if let Some(next) = (*current).next {
                 current = next;
             } else {
                 return Err(NovaError::HeapFull);
@@ -122,10 +122,12 @@ impl Heap {
                 },
             )
         };
+        unsafe {
             (*current).next = Some(new_address);
             (*current).free = false;
             (*current).size = size;
         }
+    }
 
     pub fn free(&self, pointer: *mut u8) -> Result<(), NovaError> {
         let mut segment = Self::get_header_ref_from_data_pointer(pointer);

heap/src/tests.rs

@@ -88,7 +88,9 @@ fn test_freeing_root() {
         assert_eq!((*root_header).size, root_header_start_size);
         assert!((*root_header).next.is_none());
     }
+}
 
+#[test]
 fn test_merging_free_sections() {
     let heap_vector = Box::new([0u8; HEAP_SIZE]);
     let mut heap = Heap::empty();
@@ -103,7 +105,7 @@ fn test_freeing_root() {
     let malloc1 = heap.malloc(MIN_BLOCK_SIZE).unwrap();
     let malloc_header_before = unsafe { *Heap::get_header_ref_from_data_pointer(malloc1) };
     let malloc2 = heap.malloc(MIN_BLOCK_SIZE).unwrap();
-        let malloc3 = heap.malloc(MIN_BLOCK_SIZE).unwrap();
+    let _ = heap.malloc(MIN_BLOCK_SIZE).unwrap();
 
     unsafe {
         assert!(heap.free(malloc1).is_ok());
@@ -122,4 +124,42 @@ fn test_freeing_root() {
         );
     }
 }
+
+#[test]
+fn test_first_fit() {
+    let heap_vector = Box::new([0u8; HEAP_SIZE]);
+    let mut heap = Heap::empty();
+    heap.init(
+        &heap_vector[0] as *const u8 as usize,
+        &heap_vector[HEAP_SIZE - 1] as *const u8 as usize,
+    );
+
+    let root_header = heap.start_address;
+    let root_header_start_size = unsafe { (*root_header).size };
+
+    let malloc1 = heap.malloc(MIN_BLOCK_SIZE).unwrap();
+    let malloc2 = heap.malloc(MIN_BLOCK_SIZE).unwrap();
+    let malloc3 = heap.malloc(MIN_BLOCK_SIZE * 3).unwrap();
+    let malloc4 = heap.malloc(MIN_BLOCK_SIZE).unwrap();
+
+    unsafe {
+        assert!(heap.free(malloc1).is_ok());
+        assert!(heap.free(malloc3).is_ok());
+        let malloc5 = heap.malloc(MIN_BLOCK_SIZE * 2).unwrap();
+        let malloc1_header = unsafe { *Heap::get_header_ref_from_data_pointer(malloc1) };
+
+        // First free block stays empty
+        assert!(malloc1_header.free);
+
+        // New allocation takes the first fit aka. malloc3
+        assert_eq!(malloc5, malloc3);
+
+        // If no free slot could be found, append to the end
+        let malloc6 = heap.malloc(MIN_BLOCK_SIZE * 2).unwrap();
+        assert!(malloc6 > malloc4);
+
+        // Malloc7 takes slot of Malloc1
+        let malloc7 = heap.malloc(MIN_BLOCK_SIZE).unwrap();
+        assert_eq!(malloc1, malloc7);
+    }
 }