Use Daala entropy coder to code trees.

When building with --enable-daala_ec, calls to aom_write_tree() and
 aom_read_tree() will convert a aom_tree_index structure with associated
 aom_prob probabilities into a CDF on the fly for use with the
 od_ec_encode_cdf_q15().
The number of symbols in the CDF is capped at 16, and trees that contain
 more than 16 leaf nodes are handled by splitting the most likely, e.g.,
 highest probability symbols, first and coding multiple symbols if
 necessary.

ntt-short-1:

         MEDIUM (%) HIGH (%)
    PSNR 0.000227   0.000213
 PSNRHVS 0.000215   0.000205
    SSIM 0.000229   0.000209
FASTSSIM 0.000229   0.000214

subset1:

          RATE (%)  DSNR (dB)
    PSNR -0.00026   0.00002
 PSNRHVS -0.00026   0.00002
    SSIM -0.00026   0.00001
FASTSSIM -0.00026   0.00001

Change-Id: Icb1a8cb854fd81fdd88fbe4bc6761c7eb4757dfe

aom_dsp/bitreader.h

@@ -115,7 +115,11 @@ static INLINE int aom_read_tree_bits(aom_reader *r, const aom_tree_index *tree,
 
 static INLINE int aom_read_tree(aom_reader *r, const aom_tree_index *tree,
                                 const aom_prob *probs) {
+#if CONFIG_DAALA_EC
+  return daala_read_tree_bits(r, tree, probs);
+#else
   return aom_read_tree_bits(r, tree, probs);
+#endif
 }
 
 static INLINE int aom_read_symbol(aom_reader *r, const aom_cdf_prob *cdf,

aom_dsp/bitwriter.h

@@ -91,7 +91,11 @@ static INLINE void aom_write_tree_bits(aom_writer *w, const aom_tree_index *tr,
 static INLINE void aom_write_tree(aom_writer *w, const aom_tree_index *tree,
                                   const aom_prob *probs, int bits, int len,
                                   aom_tree_index i) {
+#if CONFIG_DAALA_EC
+  daala_write_tree_bits(w, tree, probs, bits, len, i);
+#else
   aom_write_tree_bits(w, tree, probs, bits, len, i);
+#endif
 }
 
 static INLINE void aom_write_symbol(aom_writer *w, int symb,

aom_dsp/daalaboolreader.h

@@ -47,6 +47,25 @@ static INLINE int aom_daala_reader_has_error(daala_reader *r) {
   return r->ec.error;
 }
 
+static INLINE int daala_read_tree_bits(daala_reader *r,
+                                       const aom_tree_index *tree,
+                                       const aom_prob *probs) {
+  aom_tree_index i = 0;
+  do {
+    uint16_t cdf[16];
+    aom_tree_index index[16];
+    int path[16];
+    int dist[16];
+    int nsymbs;
+    int symb;
+    nsymbs = tree_to_cdf(tree, probs, i, cdf, index, path, dist);
+    symb = od_ec_decode_cdf_q15(&r->ec, cdf, nsymbs, "aom");
+    OD_ASSERT(symb >= 0 && symb < nsymbs);
+    i = index[symb];
+  } while (i > 0);
+  return -i;
+}
+
 #ifdef __cplusplus
 }  // extern "C"
 #endif

aom_dsp/daalaboolwriter.h

@@ -13,6 +13,7 @@
 #define AOM_DSP_DAALABOOLWRITER_H_
 
 #include "aom_dsp/entenc.h"
+#include "aom_dsp/prob.h"
 
 #ifdef __cplusplus
 extern "C" {
@@ -38,6 +39,45 @@ static INLINE void aom_daala_write(daala_writer *w, int bit, int prob) {
   }
 }
 
+static INLINE void daala_write_tree_bits(daala_writer *w,
+                                         const aom_tree_index *tree,
+                                         const aom_prob *probs, int bits,
+                                         int len, aom_tree_index i) {
+  aom_tree_index root;
+  root = i;
+  do {
+    uint16_t cdf[16];
+    aom_tree_index index[16];
+    int path[16];
+    int dist[16];
+    int nsymbs;
+    int symb;
+    int j;
+    /* Compute the CDF of the binary tree using the given probabilities. */
+    nsymbs = tree_to_cdf(tree, probs, root, cdf, index, path, dist);
+    /* Find the symbol to code. */
+    symb = -1;
+    for (j = 0; j < nsymbs; j++) {
+      /* If this symbol codes a leaf node,  */
+      if (index[j] <= 0) {
+        if (len == dist[j] && path[j] == bits) {
+          symb = j;
+          break;
+        }
+      } else {
+        if (len > dist[j] && path[j] == bits >> (len - dist[j])) {
+          symb = j;
+          break;
+        }
+      }
+    }
+    OD_ASSERT(symb != -1);
+    od_ec_encode_cdf_q15(&w->ec, symb, cdf, nsymbs);
+    bits &= (1 << (len - dist[symb])) - 1;
+    len -= dist[symb];
+  } while (len);
+}
+
 #ifdef __cplusplus
 }  // extern "C"
 #endif

aom_dsp/prob.c

@@ -9,8 +9,16 @@
  * PATENTS file, you can obtain it at www.aomedia.org/license/patent.
  */
 
+#if CONFIG_DAALA_EC
+#include <string.h>
+#endif
+
 #include "aom_dsp/prob.h"
 
+#if CONFIG_DAALA_EC
+#include "aom_dsp/entcode.h"
+#endif
+
 const uint8_t aom_norm[256] = {
   0, 7, 6, 6, 5, 5, 5, 5, 4, 4, 4, 4, 4, 4, 4, 4, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
   3, 3, 3, 3, 3, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
@@ -46,3 +54,153 @@ void aom_tree_merge_probs(const aom_tree_index *tree, const aom_prob *pre_probs,
                           const unsigned int *counts, aom_prob *probs) {
   tree_merge_probs_impl(0, tree, pre_probs, counts, probs);
 }
+
+#if CONFIG_DAALA_EC
+typedef struct tree_node tree_node;
+
+struct tree_node {
+  aom_tree_index index;
+  uint8_t probs[16];
+  uint8_t prob;
+  int path;
+  int len;
+  int l;
+  int r;
+  uint16_t pdf;
+};
+
+/* Compute the probability of this node in Q23 */
+static uint32_t tree_node_prob(tree_node n, int i) {
+  uint32_t prob;
+  /* 1.0 in Q23 */
+  prob = 16777216;
+  for (; i < n.len; i++) {
+    prob = prob * n.probs[i] >> 8;
+  }
+  return prob;
+}
+
+static int tree_node_cmp(tree_node a, tree_node b) {
+  int i;
+  uint32_t pa;
+  uint32_t pb;
+  for (i = 0; i < OD_MINI(a.len, b.len) && a.probs[i] == b.probs[i]; i++) {
+  }
+  pa = tree_node_prob(a, i);
+  pb = tree_node_prob(b, i);
+  return pa > pb ? 1 : pa < pb ? -1 : 0;
+}
+
+/* Given a Q15 probability for symbol subtree rooted at tree[n], this function
+    computes the probability of each symbol (defined as a node that has no
+    children). */
+static uint16_t tree_node_compute_probs(tree_node *tree, int n, uint16_t pdf) {
+  if (tree[n].l == 0) {
+    /* This prevents probability computations in Q15 that underflow from
+        producing a symbol that has zero probability. */
+    if (pdf == 0) pdf = 1;
+    tree[n].pdf = pdf;
+    return pdf;
+  } else {
+    /* We process the smaller probability first,  */
+    if (tree[n].prob < 128) {
+      uint16_t lp;
+      uint16_t rp;
+      lp = (((uint32_t)pdf) * tree[n].prob + 128) >> 8;
+      lp = tree_node_compute_probs(tree, tree[n].l, lp);
+      rp = tree_node_compute_probs(tree, tree[n].r, lp > pdf ? 0 : pdf - lp);
+      return lp + rp;
+    } else {
+      uint16_t rp;
+      uint16_t lp;
+      rp = (((uint32_t)pdf) * (256 - tree[n].prob) + 128) >> 8;
+      rp = tree_node_compute_probs(tree, tree[n].r, rp);
+      lp = tree_node_compute_probs(tree, tree[n].l, rp > pdf ? 0 : pdf - rp);
+      return lp + rp;
+    }
+  }
+}
+
+static int tree_node_extract(tree_node *tree, int n, int symb, uint16_t *pdf,
+                             aom_tree_index *index, int *path, int *len) {
+  if (tree[n].l == 0) {
+    pdf[symb] = tree[n].pdf;
+    if (index != NULL) index[symb] = tree[n].index;
+    if (path != NULL) path[symb] = tree[n].path;
+    if (len != NULL) len[symb] = tree[n].len;
+    return symb + 1;
+  } else {
+    symb = tree_node_extract(tree, tree[n].l, symb, pdf, index, path, len);
+    return tree_node_extract(tree, tree[n].r, symb, pdf, index, path, len);
+  }
+}
+
+int tree_to_cdf(const aom_tree_index *tree, const aom_prob *probs,
+                aom_tree_index root, uint16_t *cdf, aom_tree_index *index,
+                int *path, int *len) {
+  tree_node symb[2 * 16 - 1];
+  int nodes;
+  int next[16];
+  int size;
+  int nsymbs;
+  int i;
+  /* Create the root node with probability 1 in Q15. */
+  symb[0].index = root;
+  symb[0].path = 0;
+  symb[0].len = 0;
+  symb[0].l = symb[0].r = 0;
+  nodes = 1;
+  next[0] = 0;
+  size = 1;
+  nsymbs = 1;
+  while (size > 0 && nsymbs < 16) {
+    int m;
+    tree_node n;
+    aom_tree_index j;
+    uint8_t prob;
+    m = 0;
+    /* Find the internal node with the largest probability. */
+    for (i = 1; i < size; i++) {
+      if (tree_node_cmp(symb[next[i]], symb[next[m]]) > 0) m = i;
+    }
+    i = next[m];
+    memmove(&next[m], &next[m + 1], sizeof(*next) * (size - (m + 1)));
+    size--;
+    /* Split this symbol into two symbols */
+    n = symb[i];
+    j = n.index;
+    prob = probs[j >> 1];
+    /* Left */
+    n.index = tree[j];
+    n.path <<= 1;
+    n.len++;
+    n.probs[n.len - 1] = prob;
+    symb[nodes] = n;
+    if (n.index > 0) {
+      next[size++] = nodes;
+    }
+    /* Right */
+    n.index = tree[j + 1];
+    n.path += 1;
+    n.probs[n.len - 1] = 256 - prob;
+    symb[nodes + 1] = n;
+    if (n.index > 0) {
+      next[size++] = nodes + 1;
+    }
+    symb[i].prob = prob;
+    symb[i].l = nodes;
+    symb[i].r = nodes + 1;
+    nodes += 2;
+    nsymbs++;
+  }
+  /* Compute the probabilities of each symbol in Q15 */
+  tree_node_compute_probs(symb, 0, 32768);
+  /* Extract the cdf, index, path and length */
+  tree_node_extract(symb, 0, 0, cdf, index, path, len);
+  /* Convert to CDF */
+  for (i = 1; i < nsymbs; i++) {
+    cdf[i] = cdf[i - 1] + cdf[i];
+  }
+  return nsymbs;
+}
+#endif

aom_dsp/prob.h

@@ -96,6 +96,12 @@ static INLINE aom_prob mode_mv_merge_probs(aom_prob pre_prob,
 void aom_tree_merge_probs(const aom_tree_index *tree, const aom_prob *pre_probs,
                           const unsigned int *counts, aom_prob *probs);
 
+#if CONFIG_DAALA_EC
+int tree_to_cdf(const aom_tree_index *tree, const aom_prob *probs,
+                aom_tree_index root, uint16_t *cdf, aom_tree_index *ind,
+                int *pth, int *len);
+#endif
+
 DECLARE_ALIGNED(16, extern const uint8_t, aom_norm[256]);
 
 #ifdef __cplusplus