gvarianttype: avoid walking type string twice to hash

We already need to walk the string to determine the length of it, so just
hash the string at the same time.

glib/gvarianttype-private.h

@@ -64,4 +64,36 @@ _g_variant_type_equal (const GVariantType *type1,
   return TRUE;
 }
 
+static inline guint
+_g_variant_type_hash (gconstpointer type)
+{
+  const gchar *type_string = type;
+  guint value = 0;
+  gsize index = 0;
+  int brackets = 0;
+
+  do
+    {
+      value = (value << 5) - value + type_string[index];
+
+      while (type_string[index] == 'a' || type_string[index] == 'm')
+        {
+          index++;
+
+          value = (value << 5) - value + type_string[index];
+        }
+
+      if (type_string[index] == '(' || type_string[index] == '{')
+        brackets++;
+
+      else if (type_string[index] == ')' || type_string[index] == '}')
+        brackets--;
+
+      index++;
+    }
+  while (brackets);
+
+  return value;
+}
+
 G_END_DECLS

glib/gvarianttype.c

@@ -777,20 +777,9 @@ g_variant_type_is_variant (const GVariantType *type)
 guint
 g_variant_type_hash (gconstpointer type)
 {
-  const gchar *type_string;
-  guint value = 0;
-  gsize length;
-  gsize i;
-
   g_return_val_if_fail (g_variant_type_check (type), 0);
 
-  type_string = g_variant_type_peek_string (type);
+  return _g_variant_type_hash (type);
-  length = g_variant_type_get_string_length (type);
-
-  for (i = 0; i < length; i++)
-    value = (value << 5) - value + type_string[i];
-
-  return value;
 }
 
 /**