Merge "ANS: Switch from PDFs to CDFs." into nextgenv2

test/vp10_ans_test.cc

@@ -147,7 +147,7 @@ bool check_vpxbool(const PvVec &pv_vec, uint8_t *buf) {
 }
 
 const rans_sym rans_sym_tab[] = {
-    {70, 186}, {70, 116}, {100, 16}, {16, 0},
+    {16, 0}, {100, 16}, {70, 116}, {70, 186},
 };
 const int kDistinctSyms = sizeof(rans_sym_tab) / sizeof(rans_sym_tab[0]);
 
@@ -170,13 +170,9 @@ std::vector<int> ans_encode_build_vals(const rans_sym *tab, int iters) {
 
 void rans_build_dec_tab(const struct rans_sym sym_tab[],
                         rans_dec_lut dec_tab) {
-  int val = 0;
-  int i;
-  for (i = ans_p8_precision - 1; i >= 0; --i) {
-    dec_tab[i].val = val;
-    dec_tab[i].prob = sym_tab[val].prob;
-    dec_tab[i].cum_prob = sym_tab[val].cum_prob;
-    if (i == sym_tab[val].cum_prob) ++val;
+  dec_tab[0] = 0;
+  for (int i = 1; dec_tab[i - 1] < ans_p8_precision; ++i) {
+    dec_tab[i] = dec_tab[i - 1] + sym_tab[i - 1].prob;
   }
 }
 

vp10/common/ans.h

@@ -241,23 +241,16 @@ struct rans_dec_sym {
   AnsP8 cum_prob;  // not-inclusive
 };
 
-typedef struct rans_dec_sym rans_dec_lut[ans_p8_precision];
+// This is now just a boring cdf. It starts with an explict zero.
+// TODO(aconverse): Remove starting zero.
+typedef uint16_t rans_dec_lut[16];
 
-static INLINE void rans_build_dec_tab(const AnsP8 token_probs[],
-                                      rans_dec_lut dec_tab) {
-  int val = 0;
-  int cum_prob = 0;
-  int sym_end = token_probs[0];
+static INLINE void rans_build_cdf_from_pdf(const AnsP8 token_probs[],
+                                           rans_dec_lut cdf_tab) {
   int i;
-  for (i = 0; i < 256; ++i) {
-    if (i == sym_end) {
-      ++val;
-      cum_prob = sym_end;
-      sym_end += token_probs[val];
-    }
-    dec_tab[i].val = val;
-    dec_tab[i].prob = token_probs[val];
-    dec_tab[i].cum_prob = cum_prob;
+  cdf_tab[0] = 0;
+  for (i = 1; cdf_tab[i - 1] < ans_p8_precision; ++i) {
+    cdf_tab[i] = cdf_tab[i - 1] + token_probs[i - 1];
   }
 }
 
@@ -275,20 +268,32 @@ static INLINE void rans_write(struct AnsCoder *ans,
       (ans->state / p) * ans_p8_precision + ans->state % p + sym->cum_prob;
 }
 
+static INLINE void fetch_sym(struct rans_dec_sym *out, const rans_dec_lut cdf,
+                             AnsP8 rem) {
+  int i = 0;
+  // TODO(skal): if critical, could be a binary search.
+  // Or, better, an O(1) alias-table.
+  while (rem >= cdf[i]) {
+    ++i;
+  }
+  out->val = i - 1;
+  out->prob = cdf[i] - cdf[i - 1];
+  out->cum_prob = cdf[i - 1];
+}
+
 static INLINE int rans_read(struct AnsDecoder *ans,
                             const rans_dec_lut tab) {
   unsigned rem;
   unsigned quo;
-  int val;
+  struct rans_dec_sym sym;
   if (ans->state < l_base && ans->buf_offset > 0) {
     ans->state = ans->state * io_base + ans->buf[--ans->buf_offset];
   }
   quo = ans->state / ans_p8_precision;
   rem = ans->state % ans_p8_precision;
-  val = tab[rem].val;
-
-  ans->state = quo * tab[rem].prob + rem - tab[rem].cum_prob;
-  return val;
+  fetch_sym(&sym, tab, rem);
+  ans->state = quo * sym.prob + rem - sym.cum_prob;
+  return sym.val;
 }
 
 static INLINE int ans_read_init(struct AnsDecoder *const ans,

vp10/common/entropy.c

@@ -676,12 +676,12 @@ const vpx_prob vp10_pareto8_token_probs[COEFF_PROB_MODELS]
   {247, 1, 1, 1, 1, 1, 1, 1, 1, 1},
 };
 
-void vp10_build_pareto8_dec_tab(
+void vp10_build_pareto8_cdf_tab(
     const vpx_prob token_probs[COEFF_PROB_MODELS][ENTROPY_TOKENS - 2],
-    rans_dec_lut dec_tab[COEFF_PROB_MODELS]) {
+    rans_dec_lut cdf_tab[COEFF_PROB_MODELS]) {
   int p;
   for (p = 0; p < COEFF_PROB_MODELS; ++p) {
-    rans_build_dec_tab(token_probs[p], dec_tab[p]);
+    rans_build_cdf_from_pdf(token_probs[p], cdf_tab[p]);
   }
 }
 #endif  // CONFIG_ANS

vp10/common/entropy.h

@@ -170,9 +170,9 @@ extern const vpx_prob vp10_pareto8_full[COEFF_PROB_MODELS][MODEL_NODES];
 extern const vpx_prob
     vp10_pareto8_token_probs[COEFF_PROB_MODELS][ENTROPY_TOKENS - 2];
 
-void vp10_build_pareto8_dec_tab(
+void vp10_build_pareto8_cdf_tab(
     const vpx_prob token_probs[COEFF_PROB_MODELS][ENTROPY_TOKENS - 2],
-    rans_dec_lut dec_tab[COEFF_PROB_MODELS]);
+    rans_dec_lut cdf_tab[COEFF_PROB_MODELS]);
 #endif  // CONFIG_ANS
 
 typedef vpx_prob vp10_coeff_probs_model[REF_TYPES][COEF_BANDS]

vp10/common/onyxc_int.h

@@ -324,6 +324,9 @@ typedef struct VP10Common {
   // - this is intentionally not placed in FRAME_CONTEXT since it's reset upon
   // each keyframe and not used afterwards
   vpx_prob kf_y_prob[INTRA_MODES][INTRA_MODES][INTRA_MODES - 1];
+#if CONFIG_ANS
+  rans_dec_lut token_tab[COEFF_PROB_MODELS];
+#endif  // CONFIG_ANS
 } VP10_COMMON;
 
 // TODO(hkuang): Don't need to lock the whole pool after implementing atomic

vp10/decoder/decodeframe.c

@@ -1858,7 +1858,7 @@ static void decode_block(VP10Decoder *const pbi, MACROBLOCKD *const xd,
           for (col = 0; col < max_blocks_wide; col += step)
             predict_and_reconstruct_intra_block(xd,
 #if CONFIG_ANS
-                                                pbi->token_tab, tok,
+                                                cm->token_tab, tok,
 #else
                                                 r,
 #endif
@@ -1959,7 +1959,7 @@ static void decode_block(VP10Decoder *const pbi, MACROBLOCKD *const xd,
             for (col = 0; col < max_blocks_wide; col += step)
               eobtotal += reconstruct_inter_block(xd,
 #if CONFIG_ANS
-                                                  pbi->token_tab, tok,
+                                                  cm->token_tab, tok,
 #else
                                                   r,
 #endif

vp10/decoder/decoder.c

@@ -119,7 +119,7 @@ VP10Decoder *vp10_decoder_create(BufferPool *const pool) {
   vp10_loop_restoration_precal();
 #endif  // CONFIG_LOOP_RESTORATION
 #if CONFIG_ANS
-  vp10_build_pareto8_dec_tab(vp10_pareto8_token_probs, pbi->token_tab);
+  vp10_build_pareto8_cdf_tab(vp10_pareto8_token_probs, cm->token_tab);
 #endif  // CONFIG_ANS
 
   cm->error.setjmp = 0;

vp10/decoder/decoder.h

@@ -89,9 +89,6 @@ typedef struct VP10Decoder {
   int inv_tile_order;
   int need_resync;  // wait for key/intra-only frame.
   int hold_ref_buf;  // hold the reference buffer.
-#if CONFIG_ANS
-  rans_dec_lut token_tab[COEFF_PROB_MODELS];
-#endif  // CONFIG_ANS
 } VP10Decoder;
 
 int vp10_receive_compressed_data(struct VP10Decoder *pbi,

vp10/encoder/bitstream.c

@@ -634,6 +634,7 @@ static void pack_mb_tokens(vpx_writer *w,
 // This function serializes the tokens backwards both in token order and
 // bit order in each token.
 static void pack_mb_tokens_ans(struct AnsCoder *const ans,
+                               rans_dec_lut token_tab[COEFF_PROB_MODELS],
                                const TOKENEXTRA *const start,
                                const TOKENEXTRA *const stop,
                                vpx_bit_depth_t bit_depth) {
@@ -676,14 +677,10 @@ static void pack_mb_tokens_ans(struct AnsCoder *const ans,
 
       {
         struct rans_sym s;
-        int j;
-        const vpx_prob *token_probs =
-            vp10_pareto8_token_probs[p->context_tree[PIVOT_NODE] - 1];
-        s.cum_prob = 0;
-        for (j = ONE_TOKEN; j < t; ++j) {
-          s.cum_prob += token_probs[j - ONE_TOKEN];
-        }
-        s.prob = token_probs[t - ONE_TOKEN];
+        const rans_dec_lut *token_cdf =
+            &token_tab[p->context_tree[PIVOT_NODE] - 1];
+        s.cum_prob = (*token_cdf)[t - ONE_TOKEN];
+        s.prob = (*token_cdf)[t - ONE_TOKEN + 1] - s.cum_prob;
         rans_write(ans, &s);
       }
     }
@@ -2200,7 +2197,8 @@ static size_t encode_tiles(VP10_COMP *cpi, uint8_t *data_ptr,
                   NULL, NULL);
       vpx_stop_encode(&mode_bc);
       ans_write_init(&token_ans, mode_data_start + mode_bc.pos);
-      pack_mb_tokens_ans(&token_ans, tok, tok_end, cm->bit_depth);
+      pack_mb_tokens_ans(&token_ans, cm->token_tab, tok, tok_end,
+                         cm->bit_depth);
       token_section_size = ans_write_end(&token_ans);
       if (put_tile_size) {
         // size of this tile

vp10/encoder/encoder.c

@@ -1986,6 +1986,9 @@ VP10_COMP *vp10_create_compressor(VP10EncoderConfig *oxcf,
 #if CONFIG_LOOP_RESTORATION
   vp10_loop_restoration_precal();
 #endif  // CONFIG_LOOP_RESTORATION
+#if CONFIG_ANS
+  vp10_build_pareto8_cdf_tab(vp10_pareto8_token_probs, cm->token_tab);
+#endif  // CONFIG_ANS
 
   cm->error.setjmp = 0;