Refactor: Add macro LOG_SWITCHABLE_FILTERS

Change-Id: I7593ff2f8949d8bc26ca1c8577faaefb09640b59

av1/common/filter.h

@@ -33,8 +33,12 @@ extern "C" {
 
 #define SUPPORT_NONINTERPOLATING_FILTERS 0 /* turn on for experimentation */
 #define SWITCHABLE_FILTERS 5               /* Number of switchable filters */
+#define LOG_SWITCHABLE_FILTERS \
+  3 /* (1 << LOG_SWITCHABLE_FILTERS) > SWITCHABLE_FILTERS */
 #else
 #define SWITCHABLE_FILTERS 3 /* Number of switchable filters */
+#define LOG_SWITCHABLE_FILTERS \
+  2 /* (1 << LOG_SWITCHABLE_FILTERS) > SWITCHABLE_FILTERS */
 #endif                       // CONFIG_EXT_INTERP
 
 #define USE_TEMPORALFILTER_12TAP 1

av1/decoder/decodeframe.c

@@ -2239,7 +2239,7 @@ static void setup_segmentation_dequant(AV1_COMMON *const cm) {
 
 static InterpFilter read_interp_filter(struct aom_read_bit_buffer *rb) {
   return aom_rb_read_bit(rb) ? SWITCHABLE
-                             : aom_rb_read_literal(rb, 2 + CONFIG_EXT_INTERP);
+                             : aom_rb_read_literal(rb, LOG_SWITCHABLE_FILTERS);
 }
 
 static void setup_render_size(AV1_COMMON *cm, struct aom_read_bit_buffer *rb) {

av1/encoder/bitstream.c

@@ -2915,7 +2915,7 @@ static void write_interp_filter(InterpFilter filter,
                                 struct aom_write_bit_buffer *wb) {
   aom_wb_write_bit(wb, filter == SWITCHABLE);
   if (filter != SWITCHABLE)
-    aom_wb_write_literal(wb, filter, 2 + CONFIG_EXT_INTERP);
+    aom_wb_write_literal(wb, filter, LOG_SWITCHABLE_FILTERS);
 }
 
 static void fix_interp_filter(AV1_COMMON *cm, FRAME_COUNTS *counts) {