h264: fix HRD parameters parsing

The bit_rate_value_minus1 and cpb_size_value_minus1 elements
allow a wider range than get_ue_golomb() supports.  This
adds a get_ue_golomb_long() function supporting up to 31
leading zeros, which is the maximum for these syntax
elements, and uses it in decode_hrd_parameters().
Signed-off-by: Mans Rullgard <mans@mansr.com>

libavcodec/golomb.h

@@ -75,6 +75,20 @@ static inline int get_ue_golomb(GetBitContext *gb){
     }
 }
 
+/**
+ * Read an unsigned Exp-Golomb code in the range 0 to UINT32_MAX-1.
+ */
+static inline unsigned get_ue_golomb_long(GetBitContext *gb)
+{
+    unsigned buf, log;
+
+    buf = show_bits_long(gb, 32);
+    log = 31 - av_log2(buf);
+    skip_bits_long(gb, log);
+
+    return get_bits_long(gb, log + 1) - 1;
+}
+
  /**
  * read unsigned exp golomb code, constraint to a max of 31.
  * the return value is undefined if the stored value exceeds 31.

libavcodec/h264_ps.c

@@ -130,8 +130,8 @@ static inline int decode_hrd_parameters(H264Context *h, SPS *sps){
     get_bits(&s->gb, 4); /* bit_rate_scale */
     get_bits(&s->gb, 4); /* cpb_size_scale */
     for(i=0; i<cpb_count; i++){
-        get_ue_golomb(&s->gb); /* bit_rate_value_minus1 */
-        get_ue_golomb(&s->gb); /* cpb_size_value_minus1 */
+        get_ue_golomb_long(&s->gb); /* bit_rate_value_minus1 */
+        get_ue_golomb_long(&s->gb); /* cpb_size_value_minus1 */
         get_bits1(&s->gb);     /* cbr_flag */
     }
     sps->initial_cpb_removal_delay_length = get_bits(&s->gb, 5) + 1;