gstvalue: No longer store same-type intersection functions in table

The intersection function table is a legacy of 2005, when one could
register random intersection functions. This is no longer the case.

The only place where that table was used was:

* `gst_value_can_intersect()`, where it was already only used for identical
GType
* `gst_value_intersect()`, where the table iteration was insanely expensive

Instead this patch:
* Only stored intersection functions for *different* types (of which there are
only 4)
* Make gst_value_intersect directly call the same-type intersection functions
and only use the table if ever it doesn't match.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/454>

gst/gstvalue.c

@@ -6061,7 +6061,8 @@ gst_value_can_intersect (const GValue * value1, const GValue * value2)
       return TRUE;
   }
 
-  /* check registered intersect functions */
+  /* check registered intersect functions (only different gtype are checked at
+   * this point) */
   len = gst_value_intersect_funcs->len;
   for (i = 0; i < len; i++) {
     intersect_info = &g_array_index (gst_value_intersect_funcs,
@@ -6116,6 +6117,26 @@ gst_value_intersect (GValue * dest, const GValue * value1,
     return TRUE;
   }
 
+  if (type1 == type2) {
+    /* Equal type comparison */
+    if (type1 == GST_TYPE_INT_RANGE)
+      return gst_value_intersect_int_range_int_range (dest, value1, value2);
+    if (type1 == GST_TYPE_INT64_RANGE)
+      return gst_value_intersect_int64_range_int64_range (dest, value1, value2);
+    if (type1 == GST_TYPE_DOUBLE_RANGE)
+      return gst_value_intersect_double_range_double_range (dest, value1,
+          value2);
+    if (type1 == GST_TYPE_ARRAY)
+      return gst_value_intersect_array (dest, value1, value2);
+    if (type1 == GST_TYPE_FRACTION_RANGE)
+      return gst_value_intersect_fraction_range_fraction_range (dest, value1,
+          value2);
+    if (type1 == GST_TYPE_FLAG_SET)
+      return gst_value_intersect_flagset_flagset (dest, value1, value2);
+    if (type1 == GST_TYPE_STRUCTURE)
+      return gst_value_intersect_structure_structure (dest, value1, value2);
+  } else {
+    /* Different type comparison */
     len = gst_value_intersect_funcs->len;
     for (i = 0; i < len; i++) {
       intersect_info = &g_array_index (gst_value_intersect_funcs,
@@ -6127,6 +6148,7 @@ gst_value_intersect (GValue * dest, const GValue * value1,
         return intersect_info->func (dest, value2, value1);
       }
     }
+  }
 
   /* Failed to find a direct intersection, check if these are
    * GstFlagSet sub-types. */
@@ -7785,7 +7807,7 @@ G_STMT_START {                                                          \
 
 static const gint GST_VALUE_TABLE_DEFAULT_SIZE = 40;
 static const gint GST_VALUE_UNION_TABLE_DEFAULT_SIZE = 8;
-static const gint GST_VALUE_INTERSECT_TABLE_DEFAULT_SIZE = 16;
+static const gint GST_VALUE_INTERSECT_TABLE_DEFAULT_SIZE = 4;
 static const gint GST_VALUE_SUBTRACT_TABLE_DEFAULT_SIZE = 16;
 
 void
@@ -7904,29 +7926,17 @@ _priv_gst_value_initialize (void)
   g_value_register_transform_func (G_TYPE_STRING, GST_TYPE_FLAG_SET,
       gst_value_transform_string_flagset);
 
+  /* Only register intersection functions for *different* types.
+   * Identical type intersection should be specified directly in
+   * gst_value_intersect() */
   gst_value_register_intersect_func (G_TYPE_INT, GST_TYPE_INT_RANGE,
       gst_value_intersect_int_int_range);
-  gst_value_register_intersect_func (GST_TYPE_INT_RANGE, GST_TYPE_INT_RANGE,
-      gst_value_intersect_int_range_int_range);
   gst_value_register_intersect_func (G_TYPE_INT64, GST_TYPE_INT64_RANGE,
       gst_value_intersect_int64_int64_range);
-  gst_value_register_intersect_func (GST_TYPE_INT64_RANGE,
-      GST_TYPE_INT64_RANGE, gst_value_intersect_int64_range_int64_range);
   gst_value_register_intersect_func (G_TYPE_DOUBLE, GST_TYPE_DOUBLE_RANGE,
       gst_value_intersect_double_double_range);
-  gst_value_register_intersect_func (GST_TYPE_DOUBLE_RANGE,
-      GST_TYPE_DOUBLE_RANGE, gst_value_intersect_double_range_double_range);
-  gst_value_register_intersect_func (GST_TYPE_ARRAY, GST_TYPE_ARRAY,
-      gst_value_intersect_array);
   gst_value_register_intersect_func (GST_TYPE_FRACTION,
       GST_TYPE_FRACTION_RANGE, gst_value_intersect_fraction_fraction_range);
-  gst_value_register_intersect_func (GST_TYPE_FRACTION_RANGE,
-      GST_TYPE_FRACTION_RANGE,
-      gst_value_intersect_fraction_range_fraction_range);
-  gst_value_register_intersect_func (GST_TYPE_FLAG_SET, GST_TYPE_FLAG_SET,
-      gst_value_intersect_flagset_flagset);
-  gst_value_register_intersect_func (GST_TYPE_STRUCTURE, GST_TYPE_STRUCTURE,
-      gst_value_intersect_structure_structure);
 
   gst_value_register_subtract_func (G_TYPE_INT, GST_TYPE_INT_RANGE,
       gst_value_subtract_int_int_range);