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matroskamux: don't store used UIDs

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Currently, whenever we generate a 128-bit UID, we store it in a list and
return 0 if we ever encounter a collision. This is so mathematically
improbable that it's not worth checking for, so we can save memory and
time by not tracking the UID. Even if a collision happened, a list of
only 10 UIDs would be unlikely to detect it.

This article has a good description of how improbable a collision is:
https://en.wikipedia.org/wiki/Universally_unique_identifier#Collisions

https://bugzilla.gnome.org/show_bug.cgi?id=797086
This commit is contained in:
Martin Kelly 2018-09-05 16:11:00 -07:00 committed by Nicolas Dufresne
parent d9b52d1f5e
commit be05515da7
2 changed files with 2 additions and 30 deletions
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29
gst/matroska/matroska-mux.c
View file

@ -501,9 +501,6 @@ gst_matroska_mux_init (GstMatroskaMux * mux, gpointer g_class)
mux->num_v_streams = 0; mux->num_v_streams = 0;
mux->internal_toc = NULL; mux->internal_toc = NULL;
/* create used uid list */
mux->used_uids = g_array_sized_new (FALSE, FALSE, sizeof (guint64), 10);
/* initialize remaining variables */ /* initialize remaining variables */
gst_matroska_mux_reset (GST_ELEMENT (mux)); gst_matroska_mux_reset (GST_ELEMENT (mux));
} }
@ -526,8 +523,6 @@ gst_matroska_mux_finalize (GObject * object)
gst_object_unref (mux->ebml_write); gst_object_unref (mux->ebml_write);
g_free (mux->writing_app); g_free (mux->writing_app);
g_array_free (mux->used_uids, TRUE);
if (mux->internal_toc) { if (mux->internal_toc) {
gst_toc_unref (mux->internal_toc); gst_toc_unref (mux->internal_toc);
mux->internal_toc = NULL; mux->internal_toc = NULL;
@ -541,29 +536,14 @@ gst_matroska_mux_finalize (GObject * object)
* gst_matroska_mux_create_uid: * gst_matroska_mux_create_uid:
* @mux: #GstMatroskaMux to generate UID for. * @mux: #GstMatroskaMux to generate UID for.
* *
* Generate new unused track UID. * Generate new track UID.
* *
* Returns: New track UID. * Returns: New track UID.
*/ */
static guint64 static guint64
gst_matroska_mux_create_uid (GstMatroskaMux * mux) gst_matroska_mux_create_uid (GstMatroskaMux * mux)
{ {
guint64 uid = 0; return (((guint64) g_random_int ()) << 32) | g_random_int ();
while (!uid) {
guint i;
uid = (((guint64) g_random_int ()) << 32) | g_random_int ();
for (i = 0; i < mux->used_uids->len; i++) {
if (g_array_index (mux->used_uids, guint64, i) == uid) {
uid = 0;
break;
}
}
g_array_append_val (mux->used_uids, uid);
}
return uid;
} }
@ -712,11 +692,6 @@ gst_matroska_mux_reset (GstElement * element)
} }
mux->chapters_pos = 0; mux->chapters_pos = 0;
/* clear used uids */
if (mux->used_uids->len > 0) {
g_array_remove_range (mux->used_uids, 0, mux->used_uids->len);
}
} }
/** /**

3
gst/matroska/matroska-mux.h
View file

@ -140,9 +140,6 @@ struct _GstMatroskaMux {
/* Flag to ease handling of WebM specifics */ /* Flag to ease handling of WebM specifics */
gboolean is_webm; gboolean is_webm;
/* used uids */
GArray *used_uids;
}; };
typedef struct _GstMatroskaMuxClass { typedef struct _GstMatroskaMuxClass {