frame.c 29.3 KB
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979
// Copyright 2011 Google Inc. All Rights Reserved.
//
// Use of this source code is governed by a BSD-style license
// that can be found in the COPYING 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.
// -----------------------------------------------------------------------------
//
//   frame coding and analysis
//
// Author: Skal (pascal.massimino@gmail.com)

#include <assert.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>

#include "./vp8enci.h"
#include "./cost.h"

#if defined(__cplusplus) || defined(c_plusplus)
extern "C" {
#endif

#define SEGMENT_VISU 0
#define DEBUG_SEARCH 0    // useful to track search convergence

// On-the-fly info about the current set of residuals. Handy to avoid
// passing zillions of params.
typedef struct {
  int first;
  int last;
  const int16_t* coeffs;

  int coeff_type;
  ProbaArray* prob;
  StatsArray* stats;
  CostArray*  cost;
} VP8Residual;

//------------------------------------------------------------------------------
// Tables for level coding

const uint8_t VP8EncBands[16 + 1] = {
  0, 1, 2, 3, 6, 4, 5, 6, 6, 6, 6, 6, 6, 6, 6, 7,
  0  // sentinel
};

const uint8_t VP8Cat3[] = { 173, 148, 140 };
const uint8_t VP8Cat4[] = { 176, 155, 140, 135 };
const uint8_t VP8Cat5[] = { 180, 157, 141, 134, 130 };
const uint8_t VP8Cat6[] =
    { 254, 254, 243, 230, 196, 177, 153, 140, 133, 130, 129 };

//------------------------------------------------------------------------------
// Reset the statistics about: number of skips, token proba, level cost,...

static void ResetStats(VP8Encoder* const enc) {
  VP8Proba* const proba = &enc->proba_;
  VP8CalculateLevelCosts(proba);
  proba->nb_skip_ = 0;
}

//------------------------------------------------------------------------------
// Skip decision probability

#define SKIP_PROBA_THRESHOLD 250  // value below which using skip_proba is OK.

static int CalcSkipProba(uint64_t nb, uint64_t total) {
  return (int)(total ? (total - nb) * 255 / total : 255);
}

// Returns the bit-cost for coding the skip probability.
static int FinalizeSkipProba(VP8Encoder* const enc) {
  VP8Proba* const proba = &enc->proba_;
  const int nb_mbs = enc->mb_w_ * enc->mb_h_;
  const int nb_events = proba->nb_skip_;
  int size;
  proba->skip_proba_ = CalcSkipProba(nb_events, nb_mbs);
  proba->use_skip_proba_ = (proba->skip_proba_ < SKIP_PROBA_THRESHOLD);
  size = 256;   // 'use_skip_proba' bit
  if (proba->use_skip_proba_) {
    size +=  nb_events * VP8BitCost(1, proba->skip_proba_)
         + (nb_mbs - nb_events) * VP8BitCost(0, proba->skip_proba_);
    size += 8 * 256;   // cost of signaling the skip_proba_ itself.
  }
  return size;
}

//------------------------------------------------------------------------------
// Recording of token probabilities.

static void ResetTokenStats(VP8Encoder* const enc) {
  VP8Proba* const proba = &enc->proba_;
  memset(proba->stats_, 0, sizeof(proba->stats_));
}

// Record proba context used
static int Record(int bit, proba_t* const stats) {
  proba_t p = *stats;
  if (p >= 0xffff0000u) {               // an overflow is inbound.
    p = ((p + 1u) >> 1) & 0x7fff7fffu;  // -> divide the stats by 2.
  }
  // record bit count (lower 16 bits) and increment total count (upper 16 bits).
  p += 0x00010000u + bit;
  *stats = p;
  return bit;
}

// We keep the table free variant around for reference, in case.
#define USE_LEVEL_CODE_TABLE

// Simulate block coding, but only record statistics.
// Note: no need to record the fixed probas.
static int RecordCoeffs(int ctx, const VP8Residual* const res) {
  int n = res->first;
  // should be stats[VP8EncBands[n]], but it's equivalent for n=0 or 1
  proba_t* s = res->stats[n][ctx];
  if (res->last  < 0) {
    Record(0, s + 0);
    return 0;
  }
  while (n <= res->last) {
    int v;
    Record(1, s + 0);  // order of record doesn't matter
    while ((v = res->coeffs[n++]) == 0) {
      Record(0, s + 1);
      s = res->stats[VP8EncBands[n]][0];
    }
    Record(1, s + 1);
    if (!Record(2u < (unsigned int)(v + 1), s + 2)) {  // v = -1 or 1
      s = res->stats[VP8EncBands[n]][1];
    } else {
      v = abs(v);
#if !defined(USE_LEVEL_CODE_TABLE)
      if (!Record(v > 4, s + 3)) {
        if (Record(v != 2, s + 4))
          Record(v == 4, s + 5);
      } else if (!Record(v > 10, s + 6)) {
        Record(v > 6, s + 7);
      } else if (!Record((v >= 3 + (8 << 2)), s + 8)) {
        Record((v >= 3 + (8 << 1)), s + 9);
      } else {
        Record((v >= 3 + (8 << 3)), s + 10);
      }
#else
      if (v > MAX_VARIABLE_LEVEL)
        v = MAX_VARIABLE_LEVEL;

      {
        const int bits = VP8LevelCodes[v - 1][1];
        int pattern = VP8LevelCodes[v - 1][0];
        int i;
        for (i = 0; (pattern >>= 1) != 0; ++i) {
          const int mask = 2 << i;
          if (pattern & 1) Record(!!(bits & mask), s + 3 + i);
        }
      }
#endif
      s = res->stats[VP8EncBands[n]][2];
    }
  }
  if (n < 16) Record(0, s + 0);
  return 1;
}

// Collect statistics and deduce probabilities for next coding pass.
// Return the total bit-cost for coding the probability updates.
static int CalcTokenProba(int nb, int total) {
  assert(nb <= total);
  return nb ? (255 - nb * 255 / total) : 255;
}

// Cost of coding 'nb' 1's and 'total-nb' 0's using 'proba' probability.
static int BranchCost(int nb, int total, int proba) {
  return nb * VP8BitCost(1, proba) + (total - nb) * VP8BitCost(0, proba);
}

static int FinalizeTokenProbas(VP8Proba* const proba) {
  int has_changed = 0;
  int size = 0;
  int t, b, c, p;
  for (t = 0; t < NUM_TYPES; ++t) {
    for (b = 0; b < NUM_BANDS; ++b) {
      for (c = 0; c < NUM_CTX; ++c) {
        for (p = 0; p < NUM_PROBAS; ++p) {
          const proba_t stats = proba->stats_[t][b][c][p];
          const int nb = (stats >> 0) & 0xffff;
          const int total = (stats >> 16) & 0xffff;
          const int update_proba = VP8CoeffsUpdateProba[t][b][c][p];
          const int old_p = VP8CoeffsProba0[t][b][c][p];
          const int new_p = CalcTokenProba(nb, total);
          const int old_cost = BranchCost(nb, total, old_p)
                             + VP8BitCost(0, update_proba);
          const int new_cost = BranchCost(nb, total, new_p)
                             + VP8BitCost(1, update_proba)
                             + 8 * 256;
          const int use_new_p = (old_cost > new_cost);
          size += VP8BitCost(use_new_p, update_proba);
          if (use_new_p) {  // only use proba that seem meaningful enough.
            proba->coeffs_[t][b][c][p] = new_p;
            has_changed |= (new_p != old_p);
            size += 8 * 256;
          } else {
            proba->coeffs_[t][b][c][p] = old_p;
          }
        }
      }
    }
  }
  proba->dirty_ = has_changed;
  return size;
}

//------------------------------------------------------------------------------
// Finalize Segment probability based on the coding tree

static int GetProba(int a, int b) {
  const int total = a + b;
  return (total == 0) ? 255     // that's the default probability.
                      : (255 * a + total / 2) / total;  // rounded proba
}

static void SetSegmentProbas(VP8Encoder* const enc) {
  int p[NUM_MB_SEGMENTS] = { 0 };
  int n;

  for (n = 0; n < enc->mb_w_ * enc->mb_h_; ++n) {
    const VP8MBInfo* const mb = &enc->mb_info_[n];
    p[mb->segment_]++;
  }
  if (enc->pic_->stats != NULL) {
    for (n = 0; n < NUM_MB_SEGMENTS; ++n) {
      enc->pic_->stats->segment_size[n] = p[n];
    }
  }
  if (enc->segment_hdr_.num_segments_ > 1) {
    uint8_t* const probas = enc->proba_.segments_;
    probas[0] = GetProba(p[0] + p[1], p[2] + p[3]);
    probas[1] = GetProba(p[0], p[1]);
    probas[2] = GetProba(p[2], p[3]);

    enc->segment_hdr_.update_map_ =
        (probas[0] != 255) || (probas[1] != 255) || (probas[2] != 255);
    enc->segment_hdr_.size_ =
        p[0] * (VP8BitCost(0, probas[0]) + VP8BitCost(0, probas[1])) +
        p[1] * (VP8BitCost(0, probas[0]) + VP8BitCost(1, probas[1])) +
        p[2] * (VP8BitCost(1, probas[0]) + VP8BitCost(0, probas[2])) +
        p[3] * (VP8BitCost(1, probas[0]) + VP8BitCost(1, probas[2]));
  } else {
    enc->segment_hdr_.update_map_ = 0;
    enc->segment_hdr_.size_ = 0;
  }
}

//------------------------------------------------------------------------------
// helper functions for residuals struct VP8Residual.

static void InitResidual(int first, int coeff_type,
                         VP8Encoder* const enc, VP8Residual* const res) {
  res->coeff_type = coeff_type;
  res->prob  = enc->proba_.coeffs_[coeff_type];
  res->stats = enc->proba_.stats_[coeff_type];
  res->cost  = enc->proba_.level_cost_[coeff_type];
  res->first = first;
}

static void SetResidualCoeffs(const int16_t* const coeffs,
                              VP8Residual* const res) {
  int n;
  res->last = -1;
  for (n = 15; n >= res->first; --n) {
    if (coeffs[n]) {
      res->last = n;
      break;
    }
  }
  res->coeffs = coeffs;
}

//------------------------------------------------------------------------------
// Mode costs

static int GetResidualCost(int ctx0, const VP8Residual* const res) {
  int n = res->first;
  // should be prob[VP8EncBands[n]], but it's equivalent for n=0 or 1
  int p0 = res->prob[n][ctx0][0];
  const uint16_t* t = res->cost[n][ctx0];
  int cost;

  if (res->last < 0) {
    return VP8BitCost(0, p0);
  }
  cost = 0;
  while (n < res->last) {
    int v = res->coeffs[n];
    const int b = VP8EncBands[n + 1];
    ++n;
    if (v == 0) {
      // short-case for VP8LevelCost(t, 0) (note: VP8LevelFixedCosts[0] == 0):
      cost += t[0];
      t = res->cost[b][0];
      continue;
    }
    v = abs(v);
    cost += VP8BitCost(1, p0);
    cost += VP8LevelCost(t, v);
    {
      const int ctx = (v == 1) ? 1 : 2;
      p0 = res->prob[b][ctx][0];
      t = res->cost[b][ctx];
    }
  }
  // Last coefficient is always non-zero
  {
    const int v = abs(res->coeffs[n]);
    assert(v != 0);
    cost += VP8BitCost(1, p0);
    cost += VP8LevelCost(t, v);
    if (n < 15) {
      const int b = VP8EncBands[n + 1];
      const int ctx = (v == 1) ? 1 : 2;
      const int last_p0 = res->prob[b][ctx][0];
      cost += VP8BitCost(0, last_p0);
    }
  }
  return cost;
}

int VP8GetCostLuma4(VP8EncIterator* const it, const int16_t levels[16]) {
  const int x = (it->i4_ & 3), y = (it->i4_ >> 2);
  VP8Residual res;
  VP8Encoder* const enc = it->enc_;
  int R = 0;
  int ctx;

  InitResidual(0, 3, enc, &res);
  ctx = it->top_nz_[x] + it->left_nz_[y];
  SetResidualCoeffs(levels, &res);
  R += GetResidualCost(ctx, &res);
  return R;
}

int VP8GetCostLuma16(VP8EncIterator* const it, const VP8ModeScore* const rd) {
  VP8Residual res;
  VP8Encoder* const enc = it->enc_;
  int x, y;
  int R = 0;

  VP8IteratorNzToBytes(it);   // re-import the non-zero context

  // DC
  InitResidual(0, 1, enc, &res);
  SetResidualCoeffs(rd->y_dc_levels, &res);
  R += GetResidualCost(it->top_nz_[8] + it->left_nz_[8], &res);

  // AC
  InitResidual(1, 0, enc, &res);
  for (y = 0; y < 4; ++y) {
    for (x = 0; x < 4; ++x) {
      const int ctx = it->top_nz_[x] + it->left_nz_[y];
      SetResidualCoeffs(rd->y_ac_levels[x + y * 4], &res);
      R += GetResidualCost(ctx, &res);
      it->top_nz_[x] = it->left_nz_[y] = (res.last >= 0);
    }
  }
  return R;
}

int VP8GetCostUV(VP8EncIterator* const it, const VP8ModeScore* const rd) {
  VP8Residual res;
  VP8Encoder* const enc = it->enc_;
  int ch, x, y;
  int R = 0;

  VP8IteratorNzToBytes(it);  // re-import the non-zero context

  InitResidual(0, 2, enc, &res);
  for (ch = 0; ch <= 2; ch += 2) {
    for (y = 0; y < 2; ++y) {
      for (x = 0; x < 2; ++x) {
        const int ctx = it->top_nz_[4 + ch + x] + it->left_nz_[4 + ch + y];
        SetResidualCoeffs(rd->uv_levels[ch * 2 + x + y * 2], &res);
        R += GetResidualCost(ctx, &res);
        it->top_nz_[4 + ch + x] = it->left_nz_[4 + ch + y] = (res.last >= 0);
      }
    }
  }
  return R;
}

//------------------------------------------------------------------------------
// Coefficient coding

static int PutCoeffs(VP8BitWriter* const bw, int ctx, const VP8Residual* res) {
  int n = res->first;
  // should be prob[VP8EncBands[n]], but it's equivalent for n=0 or 1
  const uint8_t* p = res->prob[n][ctx];
  if (!VP8PutBit(bw, res->last >= 0, p[0])) {
    return 0;
  }

  while (n < 16) {
    const int c = res->coeffs[n++];
    const int sign = c < 0;
    int v = sign ? -c : c;
    if (!VP8PutBit(bw, v != 0, p[1])) {
      p = res->prob[VP8EncBands[n]][0];
      continue;
    }
    if (!VP8PutBit(bw, v > 1, p[2])) {
      p = res->prob[VP8EncBands[n]][1];
    } else {
      if (!VP8PutBit(bw, v > 4, p[3])) {
        if (VP8PutBit(bw, v != 2, p[4]))
          VP8PutBit(bw, v == 4, p[5]);
      } else if (!VP8PutBit(bw, v > 10, p[6])) {
        if (!VP8PutBit(bw, v > 6, p[7])) {
          VP8PutBit(bw, v == 6, 159);
        } else {
          VP8PutBit(bw, v >= 9, 165);
          VP8PutBit(bw, !(v & 1), 145);
        }
      } else {
        int mask;
        const uint8_t* tab;
        if (v < 3 + (8 << 1)) {          // VP8Cat3  (3b)
          VP8PutBit(bw, 0, p[8]);
          VP8PutBit(bw, 0, p[9]);
          v -= 3 + (8 << 0);
          mask = 1 << 2;
          tab = VP8Cat3;
        } else if (v < 3 + (8 << 2)) {   // VP8Cat4  (4b)
          VP8PutBit(bw, 0, p[8]);
          VP8PutBit(bw, 1, p[9]);
          v -= 3 + (8 << 1);
          mask = 1 << 3;
          tab = VP8Cat4;
        } else if (v < 3 + (8 << 3)) {   // VP8Cat5  (5b)
          VP8PutBit(bw, 1, p[8]);
          VP8PutBit(bw, 0, p[10]);
          v -= 3 + (8 << 2);
          mask = 1 << 4;
          tab = VP8Cat5;
        } else {                         // VP8Cat6 (11b)
          VP8PutBit(bw, 1, p[8]);
          VP8PutBit(bw, 1, p[10]);
          v -= 3 + (8 << 3);
          mask = 1 << 10;
          tab = VP8Cat6;
        }
        while (mask) {
          VP8PutBit(bw, !!(v & mask), *tab++);
          mask >>= 1;
        }
      }
      p = res->prob[VP8EncBands[n]][2];
    }
    VP8PutBitUniform(bw, sign);
    if (n == 16 || !VP8PutBit(bw, n <= res->last, p[0])) {
      return 1;   // EOB
    }
  }
  return 1;
}

static void CodeResiduals(VP8BitWriter* const bw, VP8EncIterator* const it,
                          const VP8ModeScore* const rd) {
  int x, y, ch;
  VP8Residual res;
  uint64_t pos1, pos2, pos3;
  const int i16 = (it->mb_->type_ == 1);
  const int segment = it->mb_->segment_;
  VP8Encoder* const enc = it->enc_;

  VP8IteratorNzToBytes(it);

  pos1 = VP8BitWriterPos(bw);
  if (i16) {
    InitResidual(0, 1, enc, &res);
    SetResidualCoeffs(rd->y_dc_levels, &res);
    it->top_nz_[8] = it->left_nz_[8] =
      PutCoeffs(bw, it->top_nz_[8] + it->left_nz_[8], &res);
    InitResidual(1, 0, enc, &res);
  } else {
    InitResidual(0, 3, enc, &res);
  }

  // luma-AC
  for (y = 0; y < 4; ++y) {
    for (x = 0; x < 4; ++x) {
      const int ctx = it->top_nz_[x] + it->left_nz_[y];
      SetResidualCoeffs(rd->y_ac_levels[x + y * 4], &res);
      it->top_nz_[x] = it->left_nz_[y] = PutCoeffs(bw, ctx, &res);
    }
  }
  pos2 = VP8BitWriterPos(bw);

  // U/V
  InitResidual(0, 2, enc, &res);
  for (ch = 0; ch <= 2; ch += 2) {
    for (y = 0; y < 2; ++y) {
      for (x = 0; x < 2; ++x) {
        const int ctx = it->top_nz_[4 + ch + x] + it->left_nz_[4 + ch + y];
        SetResidualCoeffs(rd->uv_levels[ch * 2 + x + y * 2], &res);
        it->top_nz_[4 + ch + x] = it->left_nz_[4 + ch + y] =
            PutCoeffs(bw, ctx, &res);
      }
    }
  }
  pos3 = VP8BitWriterPos(bw);
  it->luma_bits_ = pos2 - pos1;
  it->uv_bits_ = pos3 - pos2;
  it->bit_count_[segment][i16] += it->luma_bits_;
  it->bit_count_[segment][2] += it->uv_bits_;
  VP8IteratorBytesToNz(it);
}

// Same as CodeResiduals, but doesn't actually write anything.
// Instead, it just records the event distribution.
static void RecordResiduals(VP8EncIterator* const it,
                            const VP8ModeScore* const rd) {
  int x, y, ch;
  VP8Residual res;
  VP8Encoder* const enc = it->enc_;

  VP8IteratorNzToBytes(it);

  if (it->mb_->type_ == 1) {   // i16x16
    InitResidual(0, 1, enc, &res);
    SetResidualCoeffs(rd->y_dc_levels, &res);
    it->top_nz_[8] = it->left_nz_[8] =
      RecordCoeffs(it->top_nz_[8] + it->left_nz_[8], &res);
    InitResidual(1, 0, enc, &res);
  } else {
    InitResidual(0, 3, enc, &res);
  }

  // luma-AC
  for (y = 0; y < 4; ++y) {
    for (x = 0; x < 4; ++x) {
      const int ctx = it->top_nz_[x] + it->left_nz_[y];
      SetResidualCoeffs(rd->y_ac_levels[x + y * 4], &res);
      it->top_nz_[x] = it->left_nz_[y] = RecordCoeffs(ctx, &res);
    }
  }

  // U/V
  InitResidual(0, 2, enc, &res);
  for (ch = 0; ch <= 2; ch += 2) {
    for (y = 0; y < 2; ++y) {
      for (x = 0; x < 2; ++x) {
        const int ctx = it->top_nz_[4 + ch + x] + it->left_nz_[4 + ch + y];
        SetResidualCoeffs(rd->uv_levels[ch * 2 + x + y * 2], &res);
        it->top_nz_[4 + ch + x] = it->left_nz_[4 + ch + y] =
            RecordCoeffs(ctx, &res);
      }
    }
  }

  VP8IteratorBytesToNz(it);
}

//------------------------------------------------------------------------------
// Token buffer

#if !defined(DISABLE_TOKEN_BUFFER)

static void RecordTokens(VP8EncIterator* const it, const VP8ModeScore* const rd,
                         VP8TBuffer* const tokens) {
  int x, y, ch;
  VP8Residual res;
  VP8Encoder* const enc = it->enc_;

  VP8IteratorNzToBytes(it);
  if (it->mb_->type_ == 1) {   // i16x16
    const int ctx = it->top_nz_[8] + it->left_nz_[8];
    InitResidual(0, 1, enc, &res);
    SetResidualCoeffs(rd->y_dc_levels, &res);
    it->top_nz_[8] = it->left_nz_[8] =
        VP8RecordCoeffTokens(ctx, 1,
                             res.first, res.last, res.coeffs, tokens);
    RecordCoeffs(ctx, &res);
    InitResidual(1, 0, enc, &res);
  } else {
    InitResidual(0, 3, enc, &res);
  }

  // luma-AC
  for (y = 0; y < 4; ++y) {
    for (x = 0; x < 4; ++x) {
      const int ctx = it->top_nz_[x] + it->left_nz_[y];
      SetResidualCoeffs(rd->y_ac_levels[x + y * 4], &res);
      it->top_nz_[x] = it->left_nz_[y] =
          VP8RecordCoeffTokens(ctx, res.coeff_type,
                               res.first, res.last, res.coeffs, tokens);
      RecordCoeffs(ctx, &res);
    }
  }

  // U/V
  InitResidual(0, 2, enc, &res);
  for (ch = 0; ch <= 2; ch += 2) {
    for (y = 0; y < 2; ++y) {
      for (x = 0; x < 2; ++x) {
        const int ctx = it->top_nz_[4 + ch + x] + it->left_nz_[4 + ch + y];
        SetResidualCoeffs(rd->uv_levels[ch * 2 + x + y * 2], &res);
        it->top_nz_[4 + ch + x] = it->left_nz_[4 + ch + y] =
            VP8RecordCoeffTokens(ctx, 2,
                                 res.first, res.last, res.coeffs, tokens);
        RecordCoeffs(ctx, &res);
      }
    }
  }
  VP8IteratorBytesToNz(it);
}

#endif    // !DISABLE_TOKEN_BUFFER

//------------------------------------------------------------------------------
// ExtraInfo map / Debug function

#if SEGMENT_VISU
static void SetBlock(uint8_t* p, int value, int size) {
  int y;
  for (y = 0; y < size; ++y) {
    memset(p, value, size);
    p += BPS;
  }
}
#endif

static void ResetSSE(VP8Encoder* const enc) {
  enc->sse_[0] = 0;
  enc->sse_[1] = 0;
  enc->sse_[2] = 0;
  // Note: enc->sse_[3] is managed by alpha.c
  enc->sse_count_ = 0;
}

static void StoreSSE(const VP8EncIterator* const it) {
  VP8Encoder* const enc = it->enc_;
  const uint8_t* const in = it->yuv_in_;
  const uint8_t* const out = it->yuv_out_;
  // Note: not totally accurate at boundary. And doesn't include in-loop filter.
  enc->sse_[0] += VP8SSE16x16(in + Y_OFF, out + Y_OFF);
  enc->sse_[1] += VP8SSE8x8(in + U_OFF, out + U_OFF);
  enc->sse_[2] += VP8SSE8x8(in + V_OFF, out + V_OFF);
  enc->sse_count_ += 16 * 16;
}

static void StoreSideInfo(const VP8EncIterator* const it) {
  VP8Encoder* const enc = it->enc_;
  const VP8MBInfo* const mb = it->mb_;
  WebPPicture* const pic = enc->pic_;

  if (pic->stats != NULL) {
    StoreSSE(it);
    enc->block_count_[0] += (mb->type_ == 0);
    enc->block_count_[1] += (mb->type_ == 1);
    enc->block_count_[2] += (mb->skip_ != 0);
  }

  if (pic->extra_info != NULL) {
    uint8_t* const info = &pic->extra_info[it->x_ + it->y_ * enc->mb_w_];
    switch (pic->extra_info_type) {
      case 1: *info = mb->type_; break;
      case 2: *info = mb->segment_; break;
      case 3: *info = enc->dqm_[mb->segment_].quant_; break;
      case 4: *info = (mb->type_ == 1) ? it->preds_[0] : 0xff; break;
      case 5: *info = mb->uv_mode_; break;
      case 6: {
        const int b = (int)((it->luma_bits_ + it->uv_bits_ + 7) >> 3);
        *info = (b > 255) ? 255 : b; break;
      }
      case 7: *info = mb->alpha_; break;
      default: *info = 0; break;
    };
  }
#if SEGMENT_VISU  // visualize segments and prediction modes
  SetBlock(it->yuv_out_ + Y_OFF, mb->segment_ * 64, 16);
  SetBlock(it->yuv_out_ + U_OFF, it->preds_[0] * 64, 8);
  SetBlock(it->yuv_out_ + V_OFF, mb->uv_mode_ * 64, 8);
#endif
}

//------------------------------------------------------------------------------
//  StatLoop(): only collect statistics (number of skips, token usage, ...).
//  This is used for deciding optimal probabilities. It also modifies the
//  quantizer value if some target (size, PNSR) was specified.

#define kHeaderSizeEstimate (15 + 20 + 10)      // TODO: fix better

static void SetLoopParams(VP8Encoder* const enc, float q) {
  // Make sure the quality parameter is inside valid bounds
  if (q < 0.) {
    q = 0;
  } else if (q > 100.) {
    q = 100;
  }

  VP8SetSegmentParams(enc, q);      // setup segment quantizations and filters
  SetSegmentProbas(enc);            // compute segment probabilities

  ResetStats(enc);
  ResetTokenStats(enc);

  ResetSSE(enc);
}

static int OneStatPass(VP8Encoder* const enc, float q, VP8RDLevel rd_opt,
                       int nb_mbs, float* const PSNR, int percent_delta) {
  VP8EncIterator it;
  uint64_t size = 0;
  uint64_t distortion = 0;
  const uint64_t pixel_count = nb_mbs * 384;

  SetLoopParams(enc, q);

  VP8IteratorInit(enc, &it);
  do {
    VP8ModeScore info;
    VP8IteratorImport(&it);
    if (VP8Decimate(&it, &info, rd_opt)) {
      // Just record the number of skips and act like skip_proba is not used.
      enc->proba_.nb_skip_++;
    }
    RecordResiduals(&it, &info);
    size += info.R;
    distortion += info.D;
    if (percent_delta && !VP8IteratorProgress(&it, percent_delta))
      return 0;
  } while (VP8IteratorNext(&it, it.yuv_out_) && --nb_mbs > 0);
  size += FinalizeSkipProba(enc);
  size += FinalizeTokenProbas(&enc->proba_);
  size += enc->segment_hdr_.size_;
  size = ((size + 1024) >> 11) + kHeaderSizeEstimate;

  if (PSNR) {
    *PSNR = (float)(10.* log10(255. * 255. * pixel_count / distortion));
  }
  return (int)size;
}

// successive refinement increments.
static const int dqs[] = { 20, 15, 10, 8, 6, 4, 2, 1, 0 };

static int StatLoop(VP8Encoder* const enc) {
  const int method = enc->method_;
  const int do_search = enc->do_search_;
  const int fast_probe = ((method == 0 || method == 3) && !do_search);
  float q = enc->config_->quality;
  const int max_passes = enc->config_->pass;
  const int task_percent = 20;
  const int percent_per_pass = (task_percent + max_passes / 2) / max_passes;
  const int final_percent = enc->percent_ + task_percent;
  int pass;
  int nb_mbs;

  // Fast mode: quick analysis pass over few mbs. Better than nothing.
  nb_mbs = enc->mb_w_ * enc->mb_h_;
  if (fast_probe) {
    if (method == 3) {  // we need more stats for method 3 to be reliable.
      nb_mbs = (nb_mbs > 200) ? nb_mbs >> 1 : 100;
    } else {
      nb_mbs = (nb_mbs > 200) ? nb_mbs >> 2 : 50;
    }
  }

  // No target size: just do several pass without changing 'q'
  if (!do_search) {
    for (pass = 0; pass < max_passes; ++pass) {
      const VP8RDLevel rd_opt = (method >= 3) ? RD_OPT_BASIC : RD_OPT_NONE;
      if (!OneStatPass(enc, q, rd_opt, nb_mbs, NULL, percent_per_pass)) {
        return 0;
      }
    }
  } else {
    // binary search for a size close to target
    for (pass = 0; pass < max_passes && (dqs[pass] > 0); ++pass) {
      float PSNR;
      int criterion;
      const int size = OneStatPass(enc, q, RD_OPT_BASIC, nb_mbs, &PSNR,
                                   percent_per_pass);
#if DEBUG_SEARCH
      printf("#%d size=%d PSNR=%.2f q=%.2f\n", pass, size, PSNR, q);
#endif
      if (size == 0) return 0;
      if (enc->config_->target_PSNR > 0) {
        criterion = (PSNR < enc->config_->target_PSNR);
      } else {
        criterion = (size < enc->config_->target_size);
      }
      // dichotomize
      if (criterion) {
        q += dqs[pass];
      } else {
        q -= dqs[pass];
      }
    }
  }
  VP8CalculateLevelCosts(&enc->proba_);  // finalize costs
  return WebPReportProgress(enc->pic_, final_percent, &enc->percent_);
}

//------------------------------------------------------------------------------
// Main loops
//

static const int kAverageBytesPerMB[8] = { 50, 24, 16, 9, 7, 5, 3, 2 };

static int PreLoopInitialize(VP8Encoder* const enc) {
  int p;
  int ok = 1;
  const int average_bytes_per_MB = kAverageBytesPerMB[enc->base_quant_ >> 4];
  const int bytes_per_parts =
      enc->mb_w_ * enc->mb_h_ * average_bytes_per_MB / enc->num_parts_;
  // Initialize the bit-writers
  for (p = 0; ok && p < enc->num_parts_; ++p) {
    ok = VP8BitWriterInit(enc->parts_ + p, bytes_per_parts);
  }
  if (!ok) VP8EncFreeBitWriters(enc);  // malloc error occurred
  return ok;
}

static int PostLoopFinalize(VP8EncIterator* const it, int ok) {
  VP8Encoder* const enc = it->enc_;
  if (ok) {      // Finalize the partitions, check for extra errors.
    int p;
    for (p = 0; p < enc->num_parts_; ++p) {
      VP8BitWriterFinish(enc->parts_ + p);
      ok &= !enc->parts_[p].error_;
    }
  }

  if (ok) {      // All good. Finish up.
    if (enc->pic_->stats) {           // finalize byte counters...
      int i, s;
      for (i = 0; i <= 2; ++i) {
        for (s = 0; s < NUM_MB_SEGMENTS; ++s) {
          enc->residual_bytes_[i][s] = (int)((it->bit_count_[s][i] + 7) >> 3);
        }
      }
    }
    VP8AdjustFilterStrength(it);     // ...and store filter stats.
  } else {
    // Something bad happened -> need to do some memory cleanup.
    VP8EncFreeBitWriters(enc);
  }
  return ok;
}

//------------------------------------------------------------------------------
//  VP8EncLoop(): does the final bitstream coding.

static void ResetAfterSkip(VP8EncIterator* const it) {
  if (it->mb_->type_ == 1) {
    *it->nz_ = 0;  // reset all predictors
    it->left_nz_[8] = 0;
  } else {
    *it->nz_ &= (1 << 24);  // preserve the dc_nz bit
  }
}

int VP8EncLoop(VP8Encoder* const enc) {
  VP8EncIterator it;
  int ok = PreLoopInitialize(enc);
  if (!ok) return 0;

  StatLoop(enc);  // stats-collection loop

  VP8IteratorInit(enc, &it);
  VP8InitFilter(&it);
  do {
    VP8ModeScore info;
    const int dont_use_skip = !enc->proba_.use_skip_proba_;
    const VP8RDLevel rd_opt = enc->rd_opt_level_;

    VP8IteratorImport(&it);
    // Warning! order is important: first call VP8Decimate() and
    // *then* decide how to code the skip decision if there's one.
    if (!VP8Decimate(&it, &info, rd_opt) || dont_use_skip) {
      CodeResiduals(it.bw_, &it, &info);
    } else {   // reset predictors after a skip
      ResetAfterSkip(&it);
    }
#ifdef WEBP_EXPERIMENTAL_FEATURES
    if (enc->use_layer_) {
      VP8EncCodeLayerBlock(&it);
    }
#endif
    StoreSideInfo(&it);
    VP8StoreFilterStats(&it);
    VP8IteratorExport(&it);
    ok = VP8IteratorProgress(&it, 20);
  } while (ok && VP8IteratorNext(&it, it.yuv_out_));

  return PostLoopFinalize(&it, ok);
}

//------------------------------------------------------------------------------
// Single pass using Token Buffer.

#if !defined(DISABLE_TOKEN_BUFFER)

#define MIN_COUNT 96   // minimum number of macroblocks before updating stats

int VP8EncTokenLoop(VP8Encoder* const enc) {
  int ok;
  // Roughly refresh the proba height times per pass
  int max_count = (enc->mb_w_ * enc->mb_h_) >> 3;
  int cnt;
  VP8EncIterator it;
  VP8Proba* const proba = &enc->proba_;
  const VP8RDLevel rd_opt = enc->rd_opt_level_;

  if (max_count < MIN_COUNT) max_count = MIN_COUNT;
  cnt = max_count;

  assert(enc->num_parts_ == 1);
  assert(enc->use_tokens_);
  assert(proba->use_skip_proba_ == 0);
  assert(rd_opt >= RD_OPT_BASIC);   // otherwise, token-buffer won't be useful
  assert(!enc->do_search_);         // TODO(skal): handle pass and dichotomy

  SetLoopParams(enc, enc->config_->quality);

  ok = PreLoopInitialize(enc);
  if (!ok) return 0;

  VP8IteratorInit(enc, &it);
  VP8InitFilter(&it);
  do {
    VP8ModeScore info;
    VP8IteratorImport(&it);
    if (--cnt < 0) {
      FinalizeTokenProbas(proba);
      VP8CalculateLevelCosts(proba);  // refresh cost tables for rd-opt
      cnt = max_count;
    }
    VP8Decimate(&it, &info, rd_opt);
    RecordTokens(&it, &info, &enc->tokens_);
#ifdef WEBP_EXPERIMENTAL_FEATURES
    if (enc->use_layer_) {
      VP8EncCodeLayerBlock(&it);
    }
#endif
    StoreSideInfo(&it);
    VP8StoreFilterStats(&it);
    VP8IteratorExport(&it);
    ok = VP8IteratorProgress(&it, 20);
  } while (ok && VP8IteratorNext(&it, it.yuv_out_));

  ok = ok && WebPReportProgress(enc->pic_, enc->percent_ + 20, &enc->percent_);

  if (ok) {
    FinalizeTokenProbas(proba);
    ok = VP8EmitTokens(&enc->tokens_, enc->parts_ + 0,
                       (const uint8_t*)proba->coeffs_, 1);
  }

  return PostLoopFinalize(&it, ok);
}

#else

int VP8EncTokenLoop(VP8Encoder* const enc) {
  (void)enc;
  return 0;   // we shouldn't be here.
}

#endif    // DISABLE_TOKEN_BUFFER

//------------------------------------------------------------------------------

#if defined(__cplusplus) || defined(c_plusplus)
}    // extern "C"
#endif