vp9/encoder/vp9_subexp.c

   1 /*
   2  *  Copyright (c) 2013 The WebM project authors. All Rights Reserved.
   3  *
   4  *  Use of this source code is governed by a BSD-style license
   5  *  that can be found in the LICENSE file in the root of the source
   6  *  tree. An additional intellectual property rights grant can be found
   7  *  in the file PATENTS.  All contributing project authors may
   8  *  be found in the AUTHORS file in the root of the source tree.
   9  */
  10
  11 #include "vp9/common/vp9_common.h"
  12 #include "vp9/common/vp9_entropy.h"
  13
  14 #include "vp9/encoder/vp9_cost.h"
  15 #include "vp9/encoder/vp9_subexp.h"
  16 #include "vp9/encoder/vp9_writer.h"
  17
  18 #define vp9_cost_upd256  ((int)(vp9_cost_one(upd) - vp9_cost_zero(upd)))
  19
  20 static const int update_bits[255] = {
  21    5,  5,  5,  5,  5,  5,  5,  5,  5,  5,  5,  5,  5,  5,  5,  5,
  22    6,  6,  6,  6,  6,  6,  6,  6,  6,  6,  6,  6,  6,  6,  6,  6,
  23    8,  8,  8,  8,  8,  8,  8,  8,  8,  8,  8,  8,  8,  8,  8,  8,
  24    8,  8,  8,  8,  8,  8,  8,  8,  8,  8,  8,  8,  8,  8,  8,  8,
  25   10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10,
  26   10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10,
  27   10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10,
  28   10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10,
  29   10, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11,
  30   11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11,
  31   11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11,
  32   11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11,
  33   11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11,
  34   11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11,
  35   11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11,
  36   11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11,  0,
  37 };
  38
  39 static int recenter_nonneg(int v, int m) {
  40   if (v > (m << 1))
  41     return v;
  42   else if (v >= m)
  43     return ((v - m) << 1);
  44   else
  45     return ((m - v) << 1) - 1;
  46 }
  47
  48 static int remap_prob(int v, int m) {
  49   int i;
  50   static const int map_table[MAX_PROB - 1] = {
  51     // generated by:
  52     //   map_table[j] = split_index(j, MAX_PROB - 1, MODULUS_PARAM);
  53      20,  21,  22,  23,  24,  25,   0,  26,  27,  28,  29,  30,  31,  32,  33,
  54      34,  35,  36,  37,   1,  38,  39,  40,  41,  42,  43,  44,  45,  46,  47,
  55      48,  49,   2,  50,  51,  52,  53,  54,  55,  56,  57,  58,  59,  60,  61,
  56       3,  62,  63,  64,  65,  66,  67,  68,  69,  70,  71,  72,  73,   4,  74,
  57      75,  76,  77,  78,  79,  80,  81,  82,  83,  84,  85,   5,  86,  87,  88,
  58      89,  90,  91,  92,  93,  94,  95,  96,  97,   6,  98,  99, 100, 101, 102,
  59     103, 104, 105, 106, 107, 108, 109,   7, 110, 111, 112, 113, 114, 115, 116,
  60     117, 118, 119, 120, 121,   8, 122, 123, 124, 125, 126, 127, 128, 129, 130,
  61     131, 132, 133,   9, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144,
  62     145,  10, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157,  11,
  63     158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169,  12, 170, 171,
  64     172, 173, 174, 175, 176, 177, 178, 179, 180, 181,  13, 182, 183, 184, 185,
  65     186, 187, 188, 189, 190, 191, 192, 193,  14, 194, 195, 196, 197, 198, 199,
  66     200, 201, 202, 203, 204, 205,  15, 206, 207, 208, 209, 210, 211, 212, 213,
  67     214, 215, 216, 217,  16, 218, 219, 220, 221, 222, 223, 224, 225, 226, 227,
  68     228, 229,  17, 230, 231, 232, 233, 234, 235, 236, 237, 238, 239, 240, 241,
  69      18, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253,  19,
  70   };
  71   v--;
  72   m--;
  73   if ((m << 1) <= MAX_PROB)
  74     i = recenter_nonneg(v, m) - 1;
  75   else
  76     i = recenter_nonneg(MAX_PROB - 1 - v, MAX_PROB - 1 - m) - 1;
  77
  78   i = map_table[i];
  79   return i;
  80 }
  81
  82 static int prob_diff_update_cost(vp9_prob newp, vp9_prob oldp) {
  83   int delp = remap_prob(newp, oldp);
  84   return update_bits[delp] * 256;
  85 }
  86
  87 static void encode_uniform(vp9_writer *w, int v) {
  88   const int l = 8;
  89   const int m = (1 << l) - 191;
  90   if (v < m) {
  91     vp9_write_literal(w, v, l - 1);
  92   } else {
  93     vp9_write_literal(w, m + ((v - m) >> 1), l - 1);
  94     vp9_write_literal(w, (v - m) & 1, 1);
  95   }
  96 }
  97
  98 static INLINE int write_bit_gte(vp9_writer *w, int word, int test) {
  99   vp9_write_literal(w, word >= test, 1);
 100   return word >= test;
 101 }
 102
 103 static void encode_term_subexp(vp9_writer *w, int word) {
 104   if (!write_bit_gte(w, word, 16)) {
 105     vp9_write_literal(w, word, 4);
 106   } else if (!write_bit_gte(w, word, 32)) {
 107     vp9_write_literal(w, word - 16, 4);
 108   } else if (!write_bit_gte(w, word, 64)) {
 109     vp9_write_literal(w, word - 32, 5);
 110   } else {
 111     encode_uniform(w, word - 64);
 112   }
 113 }
 114
 115 void vp9_write_prob_diff_update(vp9_writer *w, vp9_prob newp, vp9_prob oldp) {
 116   const int delp = remap_prob(newp, oldp);
 117   encode_term_subexp(w, delp);
 118 }
 119
 120 int vp9_prob_diff_update_savings_search(const unsigned int *ct,
 121                                         vp9_prob oldp, vp9_prob *bestp,
 122                                         vp9_prob upd) {
 123   const int old_b = cost_branch256(ct, oldp);
 124   int bestsavings = 0;
 125   vp9_prob newp, bestnewp = oldp;
 126   const int step = *bestp > oldp ? -1 : 1;
 127
 128   for (newp = *bestp; newp != oldp; newp += step) {
 129     const int new_b = cost_branch256(ct, newp);
 130     const int update_b = prob_diff_update_cost(newp, oldp) + vp9_cost_upd256;
 131     const int savings = old_b - new_b - update_b;
 132     if (savings > bestsavings) {
 133       bestsavings = savings;
 134       bestnewp = newp;
 135     }
 136   }
 137   *bestp = bestnewp;
 138   return bestsavings;
 139 }
 140
 141 int vp9_prob_diff_update_savings_search_model(const unsigned int *ct,
 142                                               const vp9_prob *oldp,
 143                                               vp9_prob *bestp,
 144                                               vp9_prob upd,
 145                                               int stepsize) {
 146   int i, old_b, new_b, update_b, savings, bestsavings, step;
 147   int newp;
 148   vp9_prob bestnewp, newplist[ENTROPY_NODES], oldplist[ENTROPY_NODES];
 149   vp9_model_to_full_probs(oldp, oldplist);
 150   memcpy(newplist, oldp, sizeof(vp9_prob) * UNCONSTRAINED_NODES);
 151   for (i = UNCONSTRAINED_NODES, old_b = 0; i < ENTROPY_NODES; ++i)
 152     old_b += cost_branch256(ct + 2 * i, oldplist[i]);
 153   old_b += cost_branch256(ct + 2 * PIVOT_NODE, oldplist[PIVOT_NODE]);
 154
 155   bestsavings = 0;
 156   bestnewp = oldp[PIVOT_NODE];
 157
 158   if (*bestp > oldp[PIVOT_NODE]) {
 159     step = -stepsize;
 160     for (newp = *bestp; newp > oldp[PIVOT_NODE]; newp += step) {
 161       if (newp < 1 || newp > 255)
 162         continue;
 163       newplist[PIVOT_NODE] = newp;
 164       vp9_model_to_full_probs(newplist, newplist);
 165       for (i = UNCONSTRAINED_NODES, new_b = 0; i < ENTROPY_NODES; ++i)
 166         new_b += cost_branch256(ct + 2 * i, newplist[i]);
 167       new_b += cost_branch256(ct + 2 * PIVOT_NODE, newplist[PIVOT_NODE]);
 168       update_b = prob_diff_update_cost(newp, oldp[PIVOT_NODE]) +
 169           vp9_cost_upd256;
 170       savings = old_b - new_b - update_b;
 171       if (savings > bestsavings) {
 172         bestsavings = savings;
 173         bestnewp = newp;
 174       }
 175     }
 176   } else {
 177     step = stepsize;
 178     for (newp = *bestp; newp < oldp[PIVOT_NODE]; newp += step) {
 179       if (newp < 1 || newp > 255)
 180         continue;
 181       newplist[PIVOT_NODE] = newp;
 182       vp9_model_to_full_probs(newplist, newplist);
 183       for (i = UNCONSTRAINED_NODES, new_b = 0; i < ENTROPY_NODES; ++i)
 184         new_b += cost_branch256(ct + 2 * i, newplist[i]);
 185       new_b += cost_branch256(ct + 2 * PIVOT_NODE, newplist[PIVOT_NODE]);
 186       update_b = prob_diff_update_cost(newp, oldp[PIVOT_NODE]) +
 187           vp9_cost_upd256;
 188       savings = old_b - new_b - update_b;
 189       if (savings > bestsavings) {
 190         bestsavings = savings;
 191         bestnewp = newp;
 192       }
 193     }
 194   }
 195
 196   *bestp = bestnewp;
 197   return bestsavings;
 198 }
 199
 200 void vp9_cond_prob_diff_update(vp9_writer *w, vp9_prob *oldp,
 201                                const unsigned int ct[2]) {
 202   const vp9_prob upd = DIFF_UPDATE_PROB;
 203   vp9_prob newp = get_binary_prob(ct[0], ct[1]);
 204   const int savings = vp9_prob_diff_update_savings_search(ct, *oldp, &newp,
 205                                                           upd);
 206   assert(newp >= 1);
 207   if (savings > 0) {
 208     vp9_write(w, 1, upd);
 209     vp9_write_prob_diff_update(w, newp, *oldp);
 210     *oldp = newp;
 211   } else {
 212     vp9_write(w, 0, upd);
 213   }
 214 }