Add A1 memory allocator

src/hulk/hurl/a1.d

@@ -0,0 +1,51 @@
+/**
+ * A1 memory allocator.
+ */
+module hulk.hurl.a1;
+
+import hulk.hurl;
+import hulk.hippo;
+
+/**
+ * The A1 memory allocator is a one-shot memory allocator for kernel memory
+ * that is allocated but never freed.
+ */
+struct A1
+{
+    /**
+     * Number of bytes allocated in the A1 region so far.
+     */
+    private static __gshared size_t allocated;
+
+    /**
+     * Allocate memory.
+     *
+     * @param size
+     *   Size of memory to allocate.
+     *
+     * @return Address of allocated memory. This address will always be aligned
+     *   to a multiple of 16 bytes.
+     */
+    public static void * allocate(size_t size)
+    {
+        /* Round size up to a multiple of 16. */
+        size = (size + 0xFu) & ~0xFu;
+
+        ulong address = Hurl.A1_BASE + allocated;
+
+        ulong mapped_limit = (address + 0xFFFu) & ~0xFFFu;
+
+        allocated += size;
+
+        ulong desired_limit = (Hurl.A1_BASE + allocated + 0xFFFu) & ~0xFFFu;
+
+        while (desired_limit > mapped_limit)
+        {
+            void * page = Hippo.allocate_page();
+            Hurl.map(Hurl.A1_BASE + mapped_limit, page, PT_WRITABLE);
+            mapped_limit += PAGE_SIZE;
+        }
+
+        return cast(void *)address;
+    }
+}