codecparsers: h264: add nal_reader_skip_long() helper.

Add nal_reader_skip_long() helper function to allow an arbitrary number
of bits to be skipped. The former nal_reader_skip() function is too
limited to the actual cache size.

Use this new function to simplify gst_h264_parser_parse_sei_message()
default case, that skips unsupported payloads.

v2: made args consistent from header to source file.

Signed-off-by: Gwenole Beauchesne <gwenole.beauchesne@intel.com>

gst-libs/gst/codecparsers/gsth264parser.c

@@ -893,18 +893,13 @@ gst_h264_parser_parse_sei_message (GstH264NalParser * nalparser,
       res = gst_h264_parser_parse_pic_timing (nalparser,
           &sei->payload.pic_timing, nr);
       break;
-    default:{
+    default:
       /* Just consume payloadSize bytes, which does not account for
          emulation prevention bytes */
-      guint nbits = payload_size % 8;
+      if (!nal_reader_skip_long (nr, payload_size))
-      while (payload_size > 0) {
+        goto error;
-        nal_reader_skip (nr, nbits);
-        payload_size -= nbits;
-        nbits = 8;
-      }
       res = GST_H264_PARSER_OK;
       break;
-    }
   }
 
   /* When SEI message doesn't end at byte boundary,

gst-libs/gst/codecparsers/nalutils.c

@@ -113,9 +113,13 @@ nal_reader_read (NalReader * nr, guint nbits)
   return TRUE;
 }
 
+/* Skips the specified amount of bits. This is only suitable to a
+   cacheable number of bits */
 inline gboolean
 nal_reader_skip (NalReader * nr, guint nbits)
 {
+  g_assert (nbits <= 8 * sizeof (nr->cache));
+
   if (G_UNLIKELY (!nal_reader_read (nr, nbits)))
     return FALSE;
 
@@ -124,6 +128,24 @@ nal_reader_skip (NalReader * nr, guint nbits)
   return TRUE;
 }
 
+/* Generic version to skip any number of bits */
+gboolean
+nal_reader_skip_long (NalReader * nr, guint nbits)
+{
+  /* Leave out enough bits in the cache once we are finished */
+  const guint skip_size = 4 * sizeof (nr->cache);
+  guint remaining = nbits;
+
+  nbits %= skip_size;
+  while (remaining > 0) {
+    if (!nal_reader_skip (nr, nbits))
+      return FALSE;
+    remaining -= nbits;
+    nbits = skip_size;
+  }
+  return TRUE;
+}
+
 inline guint
 nal_reader_get_pos (const NalReader * nr)
 {

gst-libs/gst/codecparsers/nalutils.h

@@ -57,6 +57,7 @@ void nal_reader_init (NalReader * nr, const guint8 * data, guint size);
 
 gboolean nal_reader_read (NalReader * nr, guint nbits);
 gboolean nal_reader_skip (NalReader * nr, guint nbits);
+gboolean nal_reader_skip_long (NalReader * nr, guint nbits);
 guint nal_reader_get_pos (const NalReader * nr);
 guint nal_reader_get_remaining (const NalReader * nr);
 guint nal_reader_get_epb_count (const NalReader * nr);