libvpx: Pull from upstream

source/libvpx/vp9/decoder/vp9_dsubexp.c

 /*
   Copyright (c) 2010 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_entropy.h"
 
 #include "vp9/decoder/vp9_dsubexp.h"
 
 static int inv_recenter_nonneg(int v, int m) {
   if (v > 2 * m)
     return v;
 
   return v % 2 ? m - (v + 1) / 2 : m + v / 2;
 }
 
-static int decode_uniform(vp9_reader *r, int n) {
-  int v;
-  const int l = get_unsigned_bits(n);
-  const int m = (1 << l) - n;
-  if (!l)
-    return 0;
-
-  v = vp9_read_literal(r, l - 1);
+static int decode_uniform(vp9_reader *r) {
+  const int l = 8;
+  const int m = (1 << l) - 191;
+  const int v = vp9_read_literal(r, l - 1);
   return v < m ?  v : (v << 1) - m + vp9_read_bit(r);
 }
 
 
 static int merge_index(int v, int n, int modulus) {
   int max1 = (n - 1 - modulus / 2) / modulus + 1;
   if (v < max1) {
     v = v * modulus + modulus / 2;
   } else {
     int w;
@@ skipping 31 matching lines @@
   v = clamp(v, 0, 253);
   v = inv_map_table[v];
   m--;
   if ((m << 1) <= MAX_PROB) {
     return 1 + inv_recenter_nonneg(v + 1, m);
   } else {
     return MAX_PROB - inv_recenter_nonneg(v + 1, MAX_PROB - 1 - m);
   }
 }
 
-static int decode_term_subexp(vp9_reader *r, int k, int num_syms) {
-  int i = 0, mk = 0, word;
-  while (1) {
-    const int b = i ? k + i - 1 : k;
-    const int a = 1 << b;
-    if (num_syms <= mk + 3 * a) {
-      word = decode_uniform(r, num_syms - mk) + mk;
-      break;
-    } else {
-      if (vp9_read_bit(r)) {
-        i++;
-        mk += a;
-      } else {
-        word = vp9_read_literal(r, b) + mk;
-        break;
-      }
-    }
-  }
-  return word;
+static int decode_term_subexp(vp9_reader *r) {
+  if (!vp9_read_bit(r))
+    return vp9_read_literal(r, 4);
+  if (!vp9_read_bit(r))
+    return vp9_read_literal(r, 4) + 16;
+  if (!vp9_read_bit(r))
+    return vp9_read_literal(r, 5) + 32;
+  return decode_uniform(r) + 64;
 }
 
 void vp9_diff_update_prob(vp9_reader *r, vp9_prob* p) {
   if (vp9_read(r, DIFF_UPDATE_PROB)) {
-    const int delp = decode_term_subexp(r, SUBEXP_PARAM, 255);
+    const int delp = decode_term_subexp(r);
     *p = (vp9_prob)inv_remap_prob(delp, *p);
   }
 }