Disallow cm->delta_q_present_flag=1 when cm->base_qindex=0.

Delta quant doesn't make sense if the intent is to encode
the frame in lossless mode.

BUG=aomedia:393

Change-Id: Ic26e30267dd3a061d7ee5e980b6950366f06b32f

av1/decoder/decodeframe.c

@@ -4352,7 +4352,7 @@ static size_t read_uncompressed_header(AV1Decoder *pbi,
     }
 
     cm->delta_q_res = 1;
-    if (segment_quantizer_active == 0) {
+    if (segment_quantizer_active == 0 && cm->base_qindex > 0) {
       cm->delta_q_present_flag = aom_rb_read_bit(rb);
     } else {
       cm->delta_q_present_flag = 0;

av1/decoder/decodemv.c

@@ -890,6 +890,8 @@ static void read_intra_frame_mode_info(AV1_COMMON *const cm,
     xd->current_qindex =
         xd->prev_qindex +
         read_delta_qindex(cm, xd, r, mbmi, mi_col, mi_row) * cm->delta_q_res;
+    /* Normative: Clamp to [1,MAXQ] to not interfere with lossless mode */
+    xd->current_qindex = clamp(xd->current_qindex, 1, MAXQ);
     xd->prev_qindex = xd->current_qindex;
   }
 #endif
@@ -2117,6 +2119,8 @@ static void read_inter_frame_mode_info(AV1Decoder *const pbi,
     xd->current_qindex =
         xd->prev_qindex +
         read_delta_qindex(cm, xd, r, mbmi, mi_col, mi_row) * cm->delta_q_res;
+    /* Normative: Clamp to [1,MAXQ] to not interfere with lossless mode */
+    xd->current_qindex = clamp(xd->current_qindex, 1, MAXQ);
     xd->prev_qindex = xd->current_qindex;
   }
 #endif

av1/encoder/av1_quantize.c

@@ -1868,7 +1868,7 @@ void av1_init_plane_quantizers(const AV1_COMP *cpi, MACROBLOCK *x,
 
 #if CONFIG_DELTA_Q
   int current_q_index = AOMMAX(
-      0, AOMMIN(QINDEX_RANGE - 1, cpi->oxcf.aq_mode == DELTA_AQ
+      0, AOMMIN(QINDEX_RANGE - 1, cm->delta_q_present_flag
                                       ? cm->base_qindex + xd->delta_qindex
                                       : cm->base_qindex));
   const int qindex = av1_get_qindex(&cm->seg, segment_id, current_q_index);

av1/encoder/bitstream.c

@@ -1604,6 +1604,7 @@ static void pack_inter_mode_mvs(AV1_COMP *cpi, const MODE_INFO *mi,
     int super_block_upper_left =
         ((mi_row & MAX_MIB_MASK) == 0) && ((mi_col & MAX_MIB_MASK) == 0);
     if ((bsize != BLOCK_64X64 || skip == 0) && super_block_upper_left) {
+      assert(mbmi->current_q_index > 0);
       int reduced_delta_qindex =
           (mbmi->current_q_index - xd->prev_qindex) / cm->delta_q_res;
       write_delta_qindex(cm, xd, reduced_delta_qindex, w);
@@ -1971,6 +1972,7 @@ static void write_mb_modes_kf(AV1_COMMON *cm, const MACROBLOCKD *xd,
   if (cm->delta_q_present_flag) {
     int super_block_upper_left = ((mi_row & 7) == 0) && ((mi_col & 7) == 0);
     if ((bsize != BLOCK_64X64 || skip == 0) && super_block_upper_left) {
+      assert(mbmi->current_q_index > 0);
       int reduced_delta_qindex =
           (mbmi->current_q_index - xd->prev_qindex) / cm->delta_q_res;
       write_delta_qindex(cm, xd, reduced_delta_qindex, w);
@@ -4458,8 +4460,10 @@ static void write_uncompressed_header(AV1_COMP *cpi,
         segment_quantizer_active = 1;
       }
     }
-    if (segment_quantizer_active == 0) {
-      cm->delta_q_present_flag = cpi->oxcf.aq_mode == DELTA_AQ;
+
+    if (cm->delta_q_present_flag)
+      assert(segment_quantizer_active == 0 && cm->base_qindex > 0);
+    if (segment_quantizer_active == 0 && cm->base_qindex > 0) {
       aom_wb_write_bit(wb, cm->delta_q_present_flag);
       if (cm->delta_q_present_flag) {
         aom_wb_write_literal(wb, OD_ILOG_NZ(cm->delta_q_res) - 1, 2);

av1/encoder/encodeframe.c

@@ -2035,7 +2035,7 @@ static void update_stats(const AV1_COMMON *const cm, ThreadData *td, int mi_row,
     const int dq = (mbmi->current_q_index - xd->prev_qindex) / cm->delta_q_res;
     const int absdq = abs(dq);
     int i;
-    for (i = 0; i < absdq; ++i) {
+    for (i = 0; i < AOMMIN(absdq, DELTA_Q_SMALL); ++i) {
       td->counts->delta_q[i][1]++;
     }
     if (absdq < DELTA_Q_SMALL) td->counts->delta_q[absdq][0]++;
@@ -4615,7 +4615,7 @@ static void encode_rd_sb_row(AV1_COMP *cpi, ThreadData *td,
     }
 
 #if CONFIG_DELTA_Q
-    if (cpi->oxcf.aq_mode == DELTA_AQ) {
+    if (cm->delta_q_present_flag) {
       // Test mode for delta quantization
       int sb_row = mi_row >> 3;
       int sb_col = mi_col >> 3;
@@ -4627,9 +4627,11 @@ static void encode_rd_sb_row(AV1_COMP *cpi, ThreadData *td,
       int qmask = ~(cm->delta_q_res - 1);
       int current_qindex = clamp(cm->base_qindex + offset_qindex,
                                  cm->delta_q_res, 256 - cm->delta_q_res);
+
       current_qindex =
           ((current_qindex - cm->base_qindex + cm->delta_q_res / 2) & qmask) +
           cm->base_qindex;
+      assert(current_qindex > 0);
 
       xd->delta_qindex = current_qindex - cm->base_qindex;
       set_offsets(cpi, tile_info, x, mi_row, mi_col, BLOCK_64X64);
@@ -5090,6 +5092,15 @@ static void encode_frame_internal(AV1_COMP *cpi) {
   if (!cm->seg.enabled && xd->lossless[0]) x->optimize = 0;
 
   cm->tx_mode = select_tx_mode(cpi, xd);
+
+#if CONFIG_DELTA_Q
+  // Fix delta q resolution for the moment
+  cm->delta_q_res = DEFAULT_DELTA_Q_RES;
+  // Set delta_q_present_flag before it is used for the first time
+  cm->delta_q_present_flag =
+      cpi->oxcf.aq_mode == DELTA_AQ && cm->base_qindex > 0;
+#endif
+
   av1_frame_init_quantizer(cpi);
 
   av1_initialize_rd_consts(cpi);
@@ -5110,11 +5121,6 @@ static void encode_frame_internal(AV1_COMP *cpi) {
       cm->height == cm->last_height && !cm->intra_only && cm->last_show_frame;
 #endif
 
-#if CONFIG_DELTA_Q
-  // Fix delta q resolution for the moment
-  cm->delta_q_res = DEFAULT_DELTA_Q_RES;
-#endif
-
 #if CONFIG_EXT_REFS
   // NOTE(zoeliu): As cm->prev_frame can take neither a frame of
   //               show_exisiting_frame=1, nor can it take a frame not used as