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work around midi-event counter 4 byte overflow.

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This commit is contained in:
Robin Gareus 2015-12-27 02:09:54 +01:00
parent 228d6a1861
commit 2c197fd89a
1 changed files with 17 additions and 1 deletions
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18
libs/evoral/src/Event.cpp
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@ -38,7 +38,23 @@ init_event_id_counter(event_id_t n)
event_id_t
next_event_id ()
{
return g_atomic_int_add (&_event_id_counter, 1);
/* libsmf supports reading variable-length data up to 4 bytes only.
* so we wrap around at 2^(4 * 7) - 1
*
* interestingly enough libsmf happily writes data longer than that, but then
* fails to load it in ./libs/evoral/src/libsmf/smf_load.c:237
* g_critical("SMF error: Variable Length Quantities longer than four bytes are not supported yet.");
*
* event-IDs only have to be unique per .mid file.
* Previously (Ardour 4.2ish) Ardour re-generated those IDs when loading the
* file but that lead to .mid files being modified on every load/save.
*
* For now just assume that by the time 2^28 is reached, files with low ids have vanished.
* There is only one user who managed to get to 268 million events so far.
* quite a feat: id-counter="6483089" event-counter="276390506"
* Eventually a proper solution will have to be implemented.
*/
return g_atomic_int_add (&_event_id_counter, 1) & 268435455;
}
#ifdef EVORAL_EVENT_ALLOC