Doxygen for process_compound_inter_mode

BUG=aomedia:2700

Change-Id: Icf242b54378102e979e2f9dcde5926a8a5ac3caa

av1/encoder/rdopt.c

diff --git a/av1/encoder/rdopt.c b/av1/encoder/rdopt.c
index 4c4ab8b..cddd99c 100644
--- a/av1/encoder/rdopt.c
+++ b/av1/encoder/rdopt.c
@@ -2436,14 +2436,54 @@
   return 0;
 }
 
-// High level function to select all of the parameters for a compuond mode.
-// The main search functionality is done in the call to av1_compound_type_rd().
-// Returns 1 if this mode is worse than one already seen.
-// This function modifies the following:
-//     * skip_build_pred: Set to 1 if the inter predictor is built here to
-//                        avoid building it again in the future
-// TODO(sarahparker) Add documentation to variables modified by
-// av1_compound_type_rd()
+/*!\brief High level function to select parameters for compound mode.
+ *
+ * \ingroup inter_mode_search
+ * The main search functionality is done in the call to av1_compound_type_rd().
+ *
+ * \param[in]     cpi               Top-level encoder structure.
+ * \param[in]     x                 Pointer to struct holding all the data for
+ *                                  the current macroblock.
+ * \param[in]     args              HandleInterModeArgs struct holding
+ *                                  miscellaneous arguments for inter mode
+ *                                  search. See the documentation for this
+ *                                  struct for a description of each member.
+ * \param[in]     ref_best_rd       Best RD found so far for this block.
+ *                                  It is used for early termination of this
+ *                                  search if the RD exceeds this value.
+ * \param[in,out] cur_mv            Current motion vector.
+ * \param[in]     bsize             Current block size.
+ * \param[in,out] compmode_interinter_cost  RD of the selected interinter
+                                    compound mode.
+ * \param[in,out] rd_buffers        CompoundTypeRdBuffers struct to hold all
+ *                                  allocated buffers for the compound
+ *                                  predictors and masks in the compound type
+ *                                  search.
+ * \param[in,out] orig_dst          A prediction buffer to hold a computed
+ *                                  prediction. This will eventually hold the
+ *                                  final prediction, and the tmp_dst info will
+ *                                  be copied here.
+ * \param[in]     tmp_dst           A temporary prediction buffer to hold a
+ *                                  computed prediction.
+ * \param[in,out] rate_mv           The rate assiciated with the motion vectors.
+ *                                  This will be modified if a motion search is
+ *                                  done in the motion mode search.
+ * \param[in,out] rd_stats          Struct to keep track of the overall RD
+ *                                  information.
+ * \param[in,out] skip_rd           An array of length 2 where skip_rd[0] is the
+ *                                  best total RD for a skip mode so far,  and
+ *                                  skip_rd[1] is the best RD for a skip mode so
+ *                                  far in luma. This is used as a speed feature
+ *                                  to skip the transform search if the computed
+ *                                  skip RD for the current mode is not better
+ *                                  than the best skip_rd so far.
+ * \param[in,out] skip_build_pred   Indicates whether or not to build the inter
+ *                                  predictor. If this is 0, the inter predictor
+ *                                  has already been built and thus we can avoid
+ *                                  repeating computation.
+ * \return Returns 1 if this mode is worse than one already seen and 0 if it is
+ * a viable candidate.
+ */
 static int process_compound_inter_mode(
     AV1_COMP *const cpi, MACROBLOCK *x, HandleInterModeArgs *args,
     int64_t ref_best_rd, int_mv *cur_mv, BLOCK_SIZE bsize,