libvpx: Pull from upstream

source/libvpx/vp9/encoder/vp9_subexp.c

 /*
  *  Copyright (c) 2013 The WebM project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #include "vp9/common/vp9_common.h"
 #include "vp9/common/vp9_entropy.h"
 
 #include "vp9/encoder/vp9_treewriter.h"
 #include "vp9/encoder/vp9_writer.h"
 
 #define vp9_cost_upd256  ((int)(vp9_cost_one(upd) - vp9_cost_zero(upd)))
 
 static int update_bits[255];
 
-static int count_uniform(int v, int n) {
-  int l = get_unsigned_bits(n);
-  int m;
-  if (l == 0) return 0;
-  m = (1 << l) - n;
-  if (v < m)
-    return l - 1;
-  else
-    return l;
-}
-
 static int split_index(int i, int n, int modulus) {
   int max1 = (n - 1 - modulus / 2) / modulus + 1;
   if (i % modulus == modulus / 2)
     i = i / modulus;
   else
     i = max1 + i - (i + modulus - modulus / 2) / modulus;
   return i;
 }
 
 static int recenter_nonneg(int v, int m) {
@@ skipping 32 matching lines @@
   m--;
   if ((m << 1) <= MAX_PROB)
     i = recenter_nonneg(v, m) - 1;
   else
     i = recenter_nonneg(MAX_PROB - 1 - v, MAX_PROB - 1 - m) - 1;
 
   i = map_table[i];
   return i;
 }
 
-static int count_term_subexp(int word, int k, int num_syms) {
-  int count = 0;
-  int i = 0;
-  int mk = 0;
-  while (1) {
-    int b = (i ? k + i - 1 : k);
-    int a = (1 << b);
-    if (num_syms <= mk + 3 * a) {
-      count += count_uniform(word - mk, num_syms - mk);
-      break;
-    } else {
-      int t = (word >= mk + a);
-      count++;
-      if (t) {
-        i = i + 1;
-        mk += a;
-      } else {
-        count += b;
-        break;
-      }
-    }
-  }
-  return count;
+static int count_term_subexp(int word) {
+  if (word < 16)
+    return 5;
+  if (word < 32)
+    return 6;
+  if (word < 64)
+    return 8;
+  if (word < 129)
+    return 10;
+  return 11;
 }
 
 static int prob_diff_update_cost(vp9_prob newp, vp9_prob oldp) {
   int delp = remap_prob(newp, oldp);
   return update_bits[delp] * 256;
 }
 
-static void encode_uniform(vp9_writer *w, int v, int n) {
-  int l = get_unsigned_bits(n);
-  int m;
-  if (l == 0)
-    return;
-  m = (1 << l) - n;
+static void encode_uniform(vp9_writer *w, int v) {
+  const int l = 8;
+  const int m = (1 << l) - 191;
   if (v < m) {
     vp9_write_literal(w, v, l - 1);
   } else {
     vp9_write_literal(w, m + ((v - m) >> 1), l - 1);
     vp9_write_literal(w, (v - m) & 1, 1);
   }
 }
 
-static void encode_term_subexp(vp9_writer *w, int word, int k, int num_syms) {
-  int i = 0;
-  int mk = 0;
-  while (1) {
-    int b = (i ? k + i - 1 : k);
-    int a = (1 << b);
-    if (num_syms <= mk + 3 * a) {
-      encode_uniform(w, word - mk, num_syms - mk);
-      break;
-    } else {
-      int t = (word >= mk + a);
-      vp9_write_literal(w, t, 1);
-      if (t) {
-        i = i + 1;
-        mk += a;
-      } else {
-        vp9_write_literal(w, word - mk, b);
-        break;
-      }
-    }
+static INLINE int write_bit_gte(vp9_writer *w, int word, int test) {
+  vp9_write_literal(w, word >= test, 1);
+  return word >= test;
+}
+
+static void encode_term_subexp(vp9_writer *w, int word) {
+  if (!write_bit_gte(w, word, 16)) {
+    vp9_write_literal(w, word, 4);
+  } else if (!write_bit_gte(w, word, 32)) {
+    vp9_write_literal(w, word - 16, 4);
+  } else if (!write_bit_gte(w, word, 64)) {
+    vp9_write_literal(w, word - 32, 5);
+  } else {
+    encode_uniform(w, word - 64);
   }
 }
 
 void vp9_write_prob_diff_update(vp9_writer *w, vp9_prob newp, vp9_prob oldp) {
   const int delp = remap_prob(newp, oldp);
-  encode_term_subexp(w, delp, SUBEXP_PARAM, 255);
+  encode_term_subexp(w, delp);
 }
 
 void vp9_compute_update_table() {
   int i;
   for (i = 0; i < 254; i++)
-    update_bits[i] = count_term_subexp(i, SUBEXP_PARAM, 255);
+    update_bits[i] = count_term_subexp(i);
 }
 
 int vp9_prob_diff_update_savings_search(const unsigned int *ct,
                                         vp9_prob oldp, vp9_prob *bestp,
                                         vp9_prob upd) {
   const int old_b = cost_branch256(ct, oldp);
   int bestsavings = 0;
   vp9_prob newp, bestnewp = oldp;
   const int step = *bestp > oldp ? -1 : 1;
 
@@ skipping 57 matching lines @@
                                                           upd);
   assert(newp >= 1);
   if (savings > 0) {
     vp9_write(w, 1, upd);
     vp9_write_prob_diff_update(w, newp, *oldp);
     *oldp = newp;
   } else {
     vp9_write(w, 0, upd);
   }
 }