Defined the allocate function

allocator.c

@@ -96,7 +96,82 @@ void deinit_allocator(allocator_t **allocator) {
   }
 }
 
-// void *alloc(allocator_t *allocator, u64 size) {
-//   ++size;
-//   return NULL;
-// }
+void *allocate(allocator_t *allocator, u64 size) {
+  u64 min_size_required = size + sizeof(block_header) + sizeof(block_footer);
+
+  if (!allocator || allocator->used == allocator->size ||
+      min_size_required > allocator->size - allocator->used) {
+    return NULL;
+  }
+
+  block_header *header = NULL;
+
+  u64 block_index = 0;
+
+  for (u64 i = 0; i < allocator->free_count; ++i) {
+    block_header *current = allocator->free_blocks[i];
+
+    if (current->size == min_size_required) {
+      header = current;
+      block_index = i;
+      break;
+    }
+
+    if (!header || (header && current->size < header->size &&
+                    current->size > min_size_required)) {
+      header = current;
+      block_index = i;
+    }
+  }
+
+  if (header) {
+    u8 *header_start = (u8 *)header;
+
+    block_footer *footer =
+        (block_footer *)(header_start + header->size - sizeof(block_footer));
+
+    u64 old_size = header->size;
+
+    bool create_new_block = false;
+
+    // If allocating exactly the required size will leave enough memory to
+    // create another block, set the header size to min_size_required
+    if (old_size - min_size_required >
+        sizeof(block_header) + sizeof(block_footer)) {
+      header->size = min_size_required;
+
+      create_new_block = true;
+    }
+
+    header->free = false;
+
+    if (create_new_block) {
+      footer->size -= header->size;
+
+      block_header *new_header = (block_header *)(header_start + header->size);
+      new_header->size = old_size - header->size;
+      new_header->magic_01 = header->magic_01;
+      new_header->magic_02 = header->magic_02;
+      new_header->free = true;
+
+      allocator->free_blocks[block_index] = new_header;
+
+      block_footer *new_footer =
+          (block_footer *)(header_start + header->size - sizeof(block_footer));
+      new_footer->size = header->size - sizeof(block_footer);
+      new_footer->magic_01 = footer->magic_01;
+      new_footer->magic_02 = footer->magic_02;
+      new_footer->free = false;
+    } else {
+      footer->free = false;
+
+      --(allocator->free_count);
+    }
+
+    allocator->used += header->size;
+
+    return (void *)(header_start + sizeof(block_header));
+  }
+
+  return NULL;
+}