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vp10: skip unreachable cat6 token extrabits.

We have historically added new bits to cat6 whenever we added a new
transform size (or bitdepth, for that matter). However, we have
always coded these new bits regardless of the actual transform size,
which means that for smaller transforms, we code bits that cannot
possibly be set. The coding (quality) impact of this is negligible,
but the bigger issue is that this allows creating bitstreams with
coefficient values that are nonsensible and can cause int overflows,
which then de facto become part of the bitstream spec. By not coding
these bits, we remove this possibility.

See issue 1065.

Change-Id: Ib3186eca2df6a7a15ddc60c8b55af182aadd964d

--- a/vp10/decoder/detokenize.c

+++ b/vp10/decoder/detokenize.c

@@ -163,17 +163,23 @@

         case CATEGORY5_TOKEN:

           val = CAT5_MIN_VAL + read_coeff(cat5_prob, 5, r);

           break;

-        case CATEGORY6_TOKEN:

+        case CATEGORY6_TOKEN: {

+#if CONFIG_MISC_FIXES

+          const int skip_bits = TX_SIZES - 1 - tx_size;

+#else

+          const int skip_bits = 0;

+#endif

+          const uint8_t *cat6p = cat6_prob + skip_bits;

 #if CONFIG_VP9_HIGHBITDEPTH

           switch (xd->bd) {

             case VPX_BITS_8:

-              val = CAT6_MIN_VAL + read_coeff(cat6_prob, 14, r);

+              val = CAT6_MIN_VAL + read_coeff(cat6p, 14 - skip_bits, r);

               break;

             case VPX_BITS_10:

-              val = CAT6_MIN_VAL + read_coeff(cat6_prob, 16, r);

+              val = CAT6_MIN_VAL + read_coeff(cat6p, 16 - skip_bits, r);

               break;

             case VPX_BITS_12:

-              val = CAT6_MIN_VAL + read_coeff(cat6_prob, 18, r);

+              val = CAT6_MIN_VAL + read_coeff(cat6p, 18 - skip_bits, r);

               break;

             default:

               assert(0);

@@ -180,9 +186,10 @@

               return -1;

           }

 #else

-          val = CAT6_MIN_VAL + read_coeff(cat6_prob, 14, r);

+          val = CAT6_MIN_VAL + read_coeff(cat6p, 14 - skip_bits, r);

 #endif

           break;

+        }

       }

     }

     v = (val * dqv) >> dq_shift;

--- a/vp10/encoder/bitstream.c

+++ b/vp10/encoder/bitstream.c

@@ -122,8 +122,11 @@

 static void pack_mb_tokens(vpx_writer *w,

                            TOKENEXTRA **tp, const TOKENEXTRA *const stop,

-                           vpx_bit_depth_t bit_depth) {

+                           vpx_bit_depth_t bit_depth, const TX_SIZE tx) {

   TOKENEXTRA *p = *tp;

+#if !CONFIG_MISC_FIXES

+  (void) tx;

+#endif

   while (p < stop && p->token != EOSB_TOKEN) {

     const int t = p->token;

@@ -171,6 +174,12 @@

     if (b->base_val) {

       const int e = p->extra, l = b->len;

+#if CONFIG_MISC_FIXES

+      int skip_bits =

+          (b->base_val == CAT6_MIN_VAL) ? TX_SIZES - 1 - tx : 0;

+#else

+      int skip_bits = 0;

+#endif

       if (l) {

         const unsigned char *pb = b->prob;

@@ -180,7 +189,12 @@

         do {

           const int bb = (v >> --n) & 1;

-          vpx_write(w, bb, pb[i >> 1]);

+          if (skip_bits) {

+            skip_bits--;

+            assert(!bb);

+          } else {

+            vpx_write(w, bb, pb[i >> 1]);

+          }

           i = b->tree[i + bb];

         } while (n);

       }

@@ -190,7 +204,7 @@

     ++p;

   }

-  *tp = p + (p->token == EOSB_TOKEN);

+  *tp = p;

 }

 static void write_segment_id(vpx_writer *w, const struct segmentation *seg,

@@ -382,6 +396,7 @@

   const VP10_COMMON *const cm = &cpi->common;

   MACROBLOCKD *const xd = &cpi->td.mb.e_mbd;

   MODE_INFO *m;

+  int plane;

   xd->mi = cm->mi_grid_visible + (mi_row * cm->mi_stride + mi_col);

   m = xd->mi[0];

@@ -398,8 +413,16 @@

     pack_inter_mode_mvs(cpi, m, w);

   }

-  assert(*tok < tok_end);

-  pack_mb_tokens(w, tok, tok_end, cm->bit_depth);

+  if (!m->mbmi.skip) {

+    assert(*tok < tok_end);

+    for (plane = 0; plane < MAX_MB_PLANE; ++plane) {

+      TX_SIZE tx = plane ? get_uv_tx_size(&m->mbmi, &xd->plane[plane])

+                         : m->mbmi.tx_size;

+      pack_mb_tokens(w, tok, tok_end, cm->bit_depth, tx);

+      assert(*tok < tok_end && (*tok)->token == EOSB_TOKEN);

+      (*tok)++;

+    }

+  }

 }

 static void write_partition(const VP10_COMMON *const cm,

--- a/vp10/encoder/encodeframe.c

+++ b/vp10/encoder/encodeframe.c

@@ -1356,9 +1356,6 @@

   if (output_enabled) {

     update_stats(&cpi->common, td);

-

-    (*tp)->token = EOSB_TOKEN;

-    (*tp)++;

   }

 }

--- a/vp10/encoder/tokenize.c

+++ b/vp10/encoder/tokenize.c

@@ -628,8 +628,16 @@

   }

   if (!dry_run) {

+    int plane;

+

     td->counts->skip[ctx][0] += skip_inc;

-    vp10_foreach_transformed_block(xd, bsize, tokenize_b, &arg);

+

+    for (plane = 0; plane < MAX_MB_PLANE; ++plane) {

+      vp10_foreach_transformed_block_in_plane(xd, bsize, plane, tokenize_b,

+                                              &arg);

+      (*t)->token = EOSB_TOKEN;

+      (*t)++;

+    }

   } else {

     vp10_foreach_transformed_block(xd, bsize, set_entropy_context_b, &arg);

   }