Fix inter-frame film grain params

When using film grain for a shown inter-frame, there is the option to
re-use the parameters from a reference frame.  Logically, the encoder
should indicate a reference frame (using film_grain_params_ref_idx) with
the same film grain parameters as the current frame.

Previously, the encoder had a bug where it would actually choose a
reference frame where the film grain parameters did *not* match.
Furthermore, a simple use of memcmp to compare the film grain parameters
has two issues: structure packing values do not have a guaranteed value
unless the structure is initialised using memset, and two attributes of
the structure are overwritten and so their equality does not matter
(update_parameters and random_seed).

This patch replaces the use of memcmp with an equivalence checking
function for film grain parameter structures.


Change-Id: I3d97213ab8b2d77a0ac5b842100785590800a01c

aom_dsp/grain_synthesis.h

diff --git a/aom_dsp/grain_synthesis.h b/aom_dsp/grain_synthesis.h
index 7aee6f6..9155b39 100644
--- a/aom_dsp/grain_synthesis.h
+++ b/aom_dsp/grain_synthesis.h
@@ -20,6 +20,8 @@
 extern "C" {
 #endif
 
+#include <string.h>
+
 #include "aom_dsp/aom_dsp_common.h"
 #include "aom/aom_image.h"
 
@@ -28,6 +30,9 @@
  * This structure contains input parameters for film grain synthesis
  */
 typedef struct {
+  // This structure is compared element-by-element in the function
+  // av1_check_grain_params_equiv: this function must be updated if any changes
+  // are made to this structure.
   int apply_grain;
 
   int update_parameters;
@@ -79,8 +84,73 @@
   int grain_scale_shift;
 
   uint16_t random_seed;
+  // This structure is compared element-by-element in the function
+  // av1_check_grain_params_equiv: this function must be updated if any changes
+  // are made to this structure.
 } aom_film_grain_t;
 
+/*!\brief Check if two film grain parameters structs are equivalent
+ *
+ * Check if two film grain parameters are equal, except for the
+ * update_parameters and random_seed elements which are ignored.
+ *
+ * \param[in]    pa               The first set of parameters to compare
+ * \param[in]    pb               The second set of parameters to compare
+ * \return       Returns 1 if the params are equivalent, 0 otherwise
+ */
+static INLINE int av1_check_grain_params_equiv(
+    const aom_film_grain_t *const pa, const aom_film_grain_t *const pb) {
+  if (pa->apply_grain != pb->apply_grain) return 0;
+  // Don't compare update_parameters
+
+  if (pa->num_y_points != pb->num_y_points) return 0;
+  if (memcmp(pa->scaling_points_y, pb->scaling_points_y,
+             pa->num_y_points * 2 * sizeof(*pa->scaling_points_y)) != 0)
+    return 0;
+
+  if (pa->num_cb_points != pb->num_cb_points) return 0;
+  if (memcmp(pa->scaling_points_cb, pb->scaling_points_cb,
+             pa->num_cb_points * 2 * sizeof(*pa->scaling_points_cb)) != 0)
+    return 0;
+
+  if (pa->num_cr_points != pb->num_cr_points) return 0;
+  if (memcmp(pa->scaling_points_cr, pb->scaling_points_cr,
+             pa->num_cr_points * 2 * sizeof(*pa->scaling_points_cr)) != 0)
+    return 0;
+
+  if (pa->scaling_shift != pb->scaling_shift) return 0;
+  if (pa->ar_coeff_lag != pb->ar_coeff_lag) return 0;
+
+  const int num_pos = 2 * pa->ar_coeff_lag * (pa->ar_coeff_lag + 1);
+  if (memcmp(pa->ar_coeffs_y, pb->ar_coeffs_y,
+             num_pos * sizeof(*pa->ar_coeffs_y)) != 0)
+    return 0;
+  if (memcmp(pa->ar_coeffs_cb, pb->ar_coeffs_cb,
+             num_pos * sizeof(*pa->ar_coeffs_cb)) != 0)
+    return 0;
+  if (memcmp(pa->ar_coeffs_cr, pb->ar_coeffs_cr,
+             num_pos * sizeof(*pa->ar_coeffs_cr)) != 0)
+    return 0;
+
+  if (pa->ar_coeff_shift != pb->ar_coeff_shift) return 0;
+
+  if (pa->cb_mult != pb->cb_mult) return 0;
+  if (pa->cb_luma_mult != pb->cb_luma_mult) return 0;
+  if (pa->cb_offset != pb->cb_offset) return 0;
+
+  if (pa->cr_mult != pb->cr_mult) return 0;
+  if (pa->cr_luma_mult != pb->cr_luma_mult) return 0;
+  if (pa->cr_offset != pb->cr_offset) return 0;
+
+  if (pa->overlap_flag != pb->overlap_flag) return 0;
+  if (pa->clip_to_restricted_range != pb->clip_to_restricted_range) return 0;
+  if (pa->bit_depth != pb->bit_depth) return 0;
+  if (pa->chroma_scaling_from_luma != pb->chroma_scaling_from_luma) return 0;
+  if (pa->grain_scale_shift != pb->grain_scale_shift) return 0;
+
+  return 1;
+}
+
 /*!\brief Add film grain
  *
  * Add film grain to an image

av1/encoder/bitstream.c

diff --git a/av1/encoder/bitstream.c b/av1/encoder/bitstream.c
index 5a893a6..6fe8fdb 100644
--- a/av1/encoder/bitstream.c
+++ b/av1/encoder/bitstream.c
@@ -2491,7 +2491,7 @@
       assert(ref_idx != INVALID_IDX);
       const RefCntBuffer *const buf = cm->ref_frame_map[ref_idx];
       if (buf->film_grain_params_present &&
-          memcmp(pars, &buf->film_grain_params, sizeof(*pars))) {
+          av1_check_grain_params_equiv(pars, &buf->film_grain_params)) {
         break;
       }
     }