ass: use a bitmap for checking duplicate events

The loop in check_duplicate_event() essentially makes event processing
with ass_process_chunk() O(n^2). Using a bitmap instead of a loop brings
it back to O(n).

This could be interpreted as an API change: since the event list is
freely modifieable by the API user through ASS_Track public fields,
libass can't know if the internal bitmap went out of sync with the
public event list. We just redefine it so that calling
ass_process_chunk() means the API user agrees not to manipulate the
event list otherwise.

1 files changed, 5 insertions, 1 deletions

diff --git a/libass/ass.h b/libass/ass.h
index c5d0936..cbcc9f0 100644
--- a/libass/ass.h
+++ b/libass/ass.h
@@ -24,7 +24,7 @@
 #include <stdarg.h>
 #include "ass_types.h"
 
-#define LIBASS_VERSION 0x01300000
+#define LIBASS_VERSION 0x01300001
 
 #ifdef __cplusplus
 extern "C" {
@@ -562,6 +562,10 @@ void ass_process_codec_private(ASS_Track *track, char *data, int size);
 /**
  * \brief Parse a chunk of subtitle stream data. A chunk contains exactly one
  * event in Matroska format.  See the Matroska specification for details.
+ * In later libass versions (since LIBASS_VERSION==0x01300001), using this
+ * function means you agree not to modify events manually, or using other
+ * functions manipulating the event list like ass_process_data(). If you do
+ * anyway, the internal duplicate checking might break.
  * \param track track
  * \param data string to parse
  * \param size length of data