msgpack-ruby-hash-aset-optimize.diff

An experimental patch.

diff --git a/ext/msgpack/unpacker.c b/ext/msgpack/unpacker.c
index 8b1f699..6b2f7af 100644
--- a/ext/msgpack/unpacker.c
+++ b/ext/msgpack/unpacker.c
@@ -690,6 +690,12 @@ int msgpack_unpacker_read_map_header(msgpack_unpacker_t* uk, uint32_t* result_si
     return 0;
 }
 
+static int hash_update_callback(st_data_t *key, st_data_t *val, st_data_t arg, int existing)
+{
+    *val = (VALUE)arg;
+    return ST_CONTINUE;
+}
+
 int msgpack_unpacker_read(msgpack_unpacker_t* uk, size_t target_stack_depth)
 {
     while(true) {
@@ -732,7 +738,12 @@ int msgpack_unpacker_read(msgpack_unpacker_t* uk, size_t target_stack_depth)
 #endif
 #endif
                 } else {
-                    rb_hash_aset(top->object, top->key, uk->last_object);
+                    VALUE key = top->key;
+                    VALUE value = uk->last_object;
+                    if (rb_obj_class(key) == rb_cString) {
+                        key = rb_str_new_frozen(key);
+                    }
+                    st_update(rb_hash_tbl(top->object), (st_data_t)key, hash_update_callback, (st_data_t)value);
                 }
                 top->type = STACK_TYPE_MAP_KEY;
                 break;