hash.c: avoid `mrb_obj_id` to get the hash value if possible.

src/hash.c

@@ -326,8 +326,15 @@ obj_hash_code(mrb_state *mrb, mrb_value key, struct RHash *h)
   case MRB_TT_TRUE:
   case MRB_TT_FALSE:
   case MRB_TT_SYMBOL:
+    hash_code = U32(mrb_fixnum(key));
+    break;
   case MRB_TT_INTEGER:
+    if (mrb_fixnum_p(key)) {
+      hash_code = U32(mrb_fixnum(key));
+      break;
+    }
 #ifndef MRB_NO_FLOAT
+    /* fall through */
   case MRB_TT_FLOAT:
 #endif
     hash_code = U32(mrb_obj_id(key));

src/object.c

@@ -16,7 +16,7 @@ mrb_obj_eq(mrb_state *mrb, mrb_value v1, mrb_value v2)
 {
 #if defined(MRB_NAN_BOXING)
   return v1.u == v2.u;
-#elif defined(MRB_NAN_BOXING)
+#elif defined(MRB_WORD_BOXING)
   return v1.w == v2.w;
 #else  /* MRB_NO_BOXING */
   if (mrb_type(v1) != mrb_type(v2)) return FALSE;